Steam Control & Condensate Drainage for Heat Exchangers

General
Heat transfer units that use steam to produce hot water are known as indirect heaters. They are often shell and tube type heat exchangers and are generally referred to as converters, hot water generators, and instantaneous heaters.

The ASME Code for Unfired Pressure Vessels is the nationally recognized authority prescribing their construction for given temperatures and pressures. The term used varies with the heating medium and the manner of application. When these heaters use steam as the heat source they are usually called steam to water converters. In steam heated converters, the water to be heated circulates through the tubes and steam circulates in the shell surrounding the outside of the tubes. This results in condensate draining to the bottom of the heat exchanger shell as the steam gives up its latent heat.

Steam to Water Heat Exchangers
The operation of the shell and tube heat exchanger is as follows. Steam enters the heat exchanger shell through the top vapor opening and surrounds the outside of the tubes. As energy is transferred through the tubes it heats the water inside the tubes. The heat transfer condenses steam inside the shell forming condensate that drops to the bottom of the heat exchanger shell. The condensate flows through the bottom condensate outlet and into a steam trap.

The steam pressure in the heat exchanger shell has a direct correlation to the temperature of the condensate formed in the shell. The properties of saturated steam are such that the steam temperature varies with steam pressure (See Table 1 below). When the latent heat of vaporization is removed, the resulting condensate will be close to the saturation temperature.Depending on the system load, slight sub-cooling may occur from the bottom of the heat exchanger and the inlet piping to the steam trap.

The heat exchanger should be selected to operate at the minimum possible steam pressure. This allows the lowest possible condensate temperature to discharge from the steam trap and reduces the amount of flash steam in the return system. When heating fluids up to 200°F, the heat exchanger should be selected based on 2 psig steam pressure in the shell for the most efficient system operation.

TIP:
When heating fluids up to 200°F,
select heat exchanger
with 2 psi steam pressure in shell
for best efficiency.

This may require a slightly larger heat exchanger than one operating at higher pressure, however it will result in a smaller less expensive low pressure steam trap and a smaller steam regulating valve. The low pressure selection will also limit the maximum temperature that can occur inside the tubes, should the temperature controller fail in an open position.

It is standard practice to add a fouling factor in the heat exchanger selection. This fouling factor adds additional tube surface area to assure adequate heating after normal scale and corrosion deposits on the tube surfaces. A standard .0005 fouling factor will add 20 to 25% additional tube surface area. When the heat exchanger is new and the tubes are clean and shiny, the heat exchanger will operate at lower than design pressure even at full system load. For example, a new heat exchanger designed for 15 psi steam to heat water to 160 degrees will generally heat the full system load with 0 psi steam in the heat exchanger shell.

TIP:
Fouling factor assures adequate heating.
A .0005 fouling factor adds 20-25% addtional tube surface.

Heat Exchanger Selection
The heat exchanger should be selected for operation at the minimum pressure to provide the most efficient operation. The properties of saturated steam tables show a larger amount of the latent heat is available at low pressure. Less energy remains in the condensate reducing the flash steam losses. A reasonable guide would be to select a steam pressure that has a saturation temperature approximately 30°F higher than the required outlet temperature of the fluid being heated in the tubes. For fluid temperatures up to 200°F, 2 psig steam is recommended.

TIP:
Steam temperature should be selected 30°F
over heat exchanger outlet temperature.

When a high steam pressure source is used, the pressure should be reduced by installing a steam pressure regulating valve or by using a combination temperature pressure regulator. After selecting the heat exchanger, the next step should be planning the installation. The heat exchanger should be mounted high enough to allow gravity drainage of the condensate from the steam trap into a vented gravity return line. If a gravity return line is not available, a condensate pump should be installed. The heat exchanger should be mounted with a pitch toward the condensate outlet. A minimum 1/2 inch pitch per 10 foot length should be provided. The heat exchanger should also be located such that removal of the tube bundle is possible.

Steam Traps
The steam trap must be capable of completely draining the condensate from the heat exchanger shell under all operating conditions. On a heat exchanger using a modulating temperature regulator to heat fluids under 212°F, the steam pressure in the shell can be 0 psig. To assure condensate drainage, the steam trap must be mounted below the heat exchanger outlet tapping and it must drain by gravity into a vented condensate return unit. When possible, the trap should be located 15 inches below the heat exchanger outlet. The 15 inches static head to the trap inlet will provide 1/2 psig static inlet pressure to the trap when the shell steam pressure is at 0 psig.

TIP:
Trap should be located at least
15 inches below heat exchanger outlet.

The trap should be sized based on this 1/2 psig differential pressure. A safety factor of 1.5 times the calculated full load capacity should be used to handle unusual start up loads. A float and thermostatic trap is normally the best selection for a heat exchanger. The thermostatic element quickly vents the air from the heat exchanger shell. The modulating float element provides continuous condensate drainage equal to the system condensing rate.

Failure to provide complete condensate drainage will lead to poor temperature control and possible water hammer. Any lift in the condensate return piping after the trap discharge requires a positive pressure to develop in the heat exchanger shell to provide condensate drainage. For this to occur, condensate must back up in the heat exchanger shell until enough tube surface is covered by condensate to build a positive steam pressure. When the positive steam pressure develops to move the condensate through the steam trap and up the vertical return line, over heating can occur on the tube side of the heat exchanger due to the positive steam pressure remaining in the shell. This results in a wide range of outlet fluid temperatures from the heat exchanger.

A lift or back pressure in the steam trap return piping can flood the heat exchanger shell and cause severe water hammer as steam enters the flooded shell. The resulting water hammer can damage the steam trap, the steam regulating valve, the heat exchanger tubes and cause the gasket in the heat exchanger and trap to fail.

Trap Installation
The trap should be located below the heat exchanger shell to allow free flow of condensate into the trap. A strainer complete with a screen blow down valve should be installed ahead of the steam trap. A shut off valve should be provided in the trap discharge return line to isolate the unit for service. Unions should be provided to allow trap service or replacement. The return line from the trap discharge should be pitched into a vented condensate return unit.

Vacuum Breakers
Most steam to water heat exchangers provide a tapping in the shell to allow installation of a vacuum breaker. The vacuum breaker allows air to enter the shell when a induced vacuum occurs. Failure to install a vacuum breaker will allow the heat exchanger shell to operate at a negative pressure which may cause condensate to be held up in the shell. During light load, the heat exchanger will have a layer of steam at the top and air under the steam to provide just the right amount of heat. The vacuum breaker should be mounted on a vertical pipe 6 to 10” above the topping to provide a cooling leg. This will protect the vacuum breaker from dirt and extreme
temperatures.

TIP:
Install a vacuum breaker
on all steam converters.

Steam Regulator
The choice of the temperature regulating valve includes self contained temperature regulators, pilot operated regulators and pneumatic regulators.

The steam inlet pressure to the regulator must be higher than the required heat exchanger operating pressure to allow flow. The available steam pressure should be at least two times the heat exchanger operating pressure to provide modulation of the regulator for good temperature control. This will also provide the smallest size steam regulator.

TIP:
For good control,
take at least a 50% pressure drop
across the control valve.

The steam regulator should be sized based on the maximum lb./hr. of steam required by the heat exchanger. To properly size the regulator, the available inlet steam pressure and the heat exchanger design operating pressure must be known. The steam regulator should not be oversized. Oversizing the regulator may cause the temperature to overshoot and the regulator will hunt more than a properly sized regulator. The steam regulator is normally smaller than the connecting inlet and outlet steam piping.

Regulator Installation
A steam drip trap should be installed in the steam piping ahead of all steam regulating valves. Failure to install a drip trap will allow condensate to collect in the steam piping ahead of the regulator. As the regulator opens, the mix of condensate and steam passing through the regulator may cause water hammer that can destroy the diaphragms or bellows used to operate the regulator.

A steam strainer should also be installed ahead of the regulators to prevent dirt from entering the valve. Dirt can deposit on the valve seat and not allow it to close tight. The steam strainer should be installed with the screen pocket horizontally. Installation with the screen down, as commonly piped for water service, will allow a condensate pocket to form in the steam line. This condensate pocket can carry into the main valve and cause water hammer or sluggish operation.

Shut off valves, pressure gauges, a manual bypass and unions should be installed to allow proper servicing of the valves and strainers. When possible refer to the manufacturer’s installation manual for proper installation.

The temperature sensing bulb should be installed as close as possible to the heat exchanger outlet. It is important that the full length of the temperature sensing bulb be inserted in the system piping. Any portion of the bulb installed in a no flow area will reduce the accuracy of temperature control. When the sensing bulb is installed in a separable well, heat transfer compound must be installed between the well and the sensing bulb to aid heat transfer. The tube side of the heat exchanger should have a continuous running recirculation pump to provide continuous flow past the sensing bulb. A minimum 20% recirculation should be provided.

Pilot operated regulators with a pressure pilot require a downstream pressure sensing line. The pressure sensing line connection should be connected in a nonturbulent area downstream of the main valve; a minimum 10 pipe diameters downstream of the main valve is recommended. The steam pressure sensing connection can also be connected directly to the heat exchanger shell.

Condensate Coolers
When heat exchangers operate at high pressure, consideration should be given to the addition of a condensate cooler. The justification will be depend on the size of the heat exchanger and the actual number of hours per day the unit will be in operation.

With a condensate cooler, the discharge from the steam trap on the steam heat exchanger outlet is piped through a water-to-water heat exchanger. A second trap is then installed on the discharge of the water-to-water heat exchanger to maintain saturation pressure and prevent flashing and water hammer from occurring in the condensate cooler. A separate thermostatic trap is installed to allow direct air venting of the steam heat exchanger into the vented return line downstream of the condensate cooler.

The water-to-water heat exchanger design differs from a steam heat exchanger. The water-to-water heat exchanger has internal baffles to direct the water flow across the tubes to improve heat transfer. Water-to-water heat exchangers are externally distinguishable as the shell inlet and outlet tappings are the same size; steam heat exchangers have a large vapor opening in the top of the shell and a smaller condensate outlet in the bottom.

The fluid in the condensate cooler tubes may be the inlet water to the steam heat exchanger tubes. When the initial temperature of the fluid is too high to cool the condensate below 212°F, a separate fluid may be heated. Preheating domestic hot water or preheating boiler make up water are two possibilities.

Heat exchanger installations depending on
operating pressures and the of type of return pump.

Low Pressure (2 psig or less) with Standard Condensate Unit

Heat exchangers operating at 2 psig or less can be drained into a standard low cost floor mounted condensate returned pump.

High Pressure with Flash Tank and Low NPSH Condensate Unit

Heat exchangers operating at higher pressure require a flash tank to vent the flash steam. An elevated condensate pump unit equipped with 2-foot NPSH pumps are required to handle the condensate at saturation temperature.

High Pressure with Condensate Cooler
and Standard Condensate Unit

When it is necessary to operate a heat exchanger at high pressure (above 15 psig) a condensate cooler can be added to sub-cool the condensate below 212°F. The illustration shows the proper steam trapping for a condensate cooler.

The incoming fluid to the steam heat exchanger may be used to sub-cool if the temperature is low enough. A separate cooling source may also be used.

Low Pressure and Pressure Powered Pump

A pressure powered pump unit may also be used to return condensate. The installation shown would be used on low pressure heat exchangers. The receiver tank is vented to atmosphere on this unit.

High Pressure and Pressure Powered Pump

Heat exchangers operating at higher pressures may use a closed pressure powered pump system. The installation shown will allow condensate to discharge directly through the steam trap when the pressure on the heat exchanger is higher than the return line pressure. When the heat exchanger pressure is not sufficient, the pressure powered pump receiver will fill and operate to discharge condensate. The F&T steam trap can be sized based on the differential pressure from the pressure powered pump discharge pressure less the return line back pressure.

Condensate Drainage - Recommended Piping

When using heaters with a modulating control valve, it is most important not to attempt to lift condensate from the float and thermostatic traps. Attempting to lift condensate leads to poor temperature control. Any condensate lifting will be from the bottom and the lift line will always be full of condensate. If the lift line is higher than the submerged coil, the coil will flood with condensate whenever the modulating control valves closes. This will result in temperature overshoot, as the hot condensate will transfer heat through the coil and over heat the water.

It is necessary for the designer/installer to make provisions to drain the condensate by gravity or into either an electric or pressure powered condensate pump. All Cemline heaters are
furnished with modulating control valves and as these valves close, the steam pressure in the coil is reduced to zero psig.

An example follows. A heater designed to operate on 15 psig steam is installed in an improperly designed system with 10 feet of condensate lift. A 10-foot column of water will have a pressure of 4.5 psig. The pressure drop across the valve will typically be 30%. This means the maximum pressure in the coil head is 10.5 psig. The steam condensing in the coil will further reduce the pressure in the coil to a pressure less than the 4.5 psig required to lift the condensate. The heater will stall until no more steam can enter because the back pressure from the 10-ft head of the condensate is greater than the available pressure in the coil. The valve, sensing the temperature in the heater is dropping, opens wider which allows more pressure into the coil and overcomes the 4.5 psig and lifts some of the condensate. This influx of steam will bring the heater to the set and as the control valve closes, the pressure in the coil goes to zero psig. As soon as the pressure drops below 4.5 psig, no more condensate is removed from the coil and the 10-ft head of condensate will then back feed through the trap and flood the coil with 250 degree F condensate. The coil transfers the heat from the 250 degree con condensate to the domestic water, resulting in an over temperature condition in the heater.

It is the responsibility of the designer/installer to properly drain the condensate. Cemline Corporation is represented by trained, expert sales agents in steam systems. Please contact the factory or one of our sales agents for assistance.

Remember, Do not attempt to lift the condensate from a water heater or Unfired Steam Generator.

SOURCE: www.cemline.com/liftcond.asp
posted by permission of Cemline

Energy Efficient Selection of Steam-to-Liquid Heat Transfer Systems

System Solutions from ITT Residential & Commercial Water Group ...

Engineered Steam-to-Liquid Heat Transfer Systems

Traditionally, the engineering of steam-to-liquid heat transfer systems has been done by using the maximum available steam pressure to select the smallest and least expensive heat exchanger. The control valve, steam trap and other ancillary equipment would then be selected using the operating conditions of this heat exchanger. While this method works, there is a better way.

It is now possible to reduce both initial equipment costs and operating costs. This is done by selecting the components of the entire system at the same time. Your ITT R&CWG Representative can now optimize your steam-to-liquid heat transfer systems with each component working together in a manner that optimizes the system as a whole.

Optimizing The System As A Whole:
Let’s take an example. Say we have 90 psig steam pressure available for a heat transfer application and use a low pressure drop control valve—10 psig ÆP—to select a heat exchanger with minimal size and surface area.

At a high steam operating pressure, there is less latent heat available for the heat exchanger, while downstream of the heat
exchanger, a higher percentage of flash steam is produced. This flash steam results from re-evaporation of the condensate when it is exposed to lower pressure or vented return lines.

In this type of system, a flash tank may be required to handle this re-evaporation, and high temperature condensate return systems may be required to pump the condensate discharging from the flash tank.

The net result of using high steam pressure at the heat exchanger is flash steam losses causing wasted energy ($), lower system efficiency ($$), and extra equipment to handle higher temperature returns ($$$). But we did save initial costs by selecting the smallest heat exchanger....? Not necessarily!

When we re-select the same application but use a steam pressure regulator to reduce the steam pressure at the heat exchanger to 5 psig, the size of the heat exchanger will increase. However, the heat exchanger cost is only part of the system cost.

By reducing steam pressure at the heat exchanger, the steam control valve may decrease in size, lowering its initial cost. Also, the steam trap may become lower in cost because of the reduced operating pressure. By lowering your steam pressure, the result may be a net savings on your initial equipment cost.

But there’s more. By using the reduced steam pressure of 5 psig, we have more latent heat available in the heat exchanger, and thus a lower percentage of flash steam. This may allow for elimination of the flash tank and conversion of the high temperature condensate return unit to a lower cost, conventional condensate return unit.

The net result: lower initial costs—and most importantly, lower operating costs yielding annual cost savings that greatly increase payback. See the example below for a typical
comparison.

Your ITT R&CWG Representative can select an engineered steam-to-liquid heat transfer system that operates efficiently, effectively, and possibly at a lower initial cost because they fully understand all of the critical components involved.

Your ITT R&CWG Representative handles Bell & Gossett heat exchangers, pumps and air control equipment; Hoffman steam control valves, regulators, safety valves, steam traps, vacuum breakers and strainers; and Domestic condensate return and boiler feed pumps. Count on your representative for the right combination of training, expertise and tools to pull it all
together in a system that suits your application exactly, using the award-winning ESP-PLUS system evaluation and equipment selection program.

Using our example steam pressures, let’s assume our heat exchanger requires 3,000 lbs/hr of steam, operates 14 hours a day for 250 days per year and the condensate goes to a vented condensate receiver at 0 psig atmospheric pressure. We will assume our steam costs $6.50 per 1000 lbs.

NET ANUAL SAVINGS FROM REDUCING PRESSURE
1,071,000 lbs of steam or $6,961.00

Specifications For:
Furnish and install according to manufacturer’s instructions, one ITT Fluid Handling energy efficient steam-to-liquid heat transfer component system, which shall have the capacity to heat _________ GPM of _________ (fluid) from _________ °F (temperature) to _________ °F (temperature) when supplied with _________ psig saturated (or degrees superheated) steam to the steam regulator. The heat exchanger shall be sized for maximum _________psig inlet pressure. The system is to have a maximum of _________ % flash steam. Energy loss calculations shall be furnished to the engineer for approval and shall include annual dollar operating costs at design conditions.

The energy efficient steam heat exchanger component system shall be piped in the field with all necessary valves, pipe and fittings, according to plans and specifications and shall consist of the following major components:

1. Hoffman Series 2000/1140 (pneumatic or self-contained) modulating steam control valve.
2. Hoffman F&T trap and “Y” strainer for the drip leg.
3. Bell & Gossett “SU” type heat exchanger with _________ fouling factor, ASME constructed with signed U-1 form per heat exchanger specification.
4. Hoffman vacuum breaker for the heat exchanger.
5. Hoffman "Y" Strainer and F&T Trap for the heat exchanger. (F&T Trap size based on 0.5 psig differential pressure with 1.5 min. safety factor.) Trap installed a minimum of 15" below the heat exchanger.
6. Optional components
   • _________ steam safety relief valve
   • _________ gauges, high pressure cocks and pigtails
   • _________ thermometers
   • _________ Bell & Gossett circulating pumps for liquid (primary/secondary) system with flow measuring and balancing valves
   • _________ ASME relief valve for system liquid.
   • _________ factory piped and frame mounted construction or individual components shall be specified.
7. __________ Duplex Domestic/Hoffman condensate return unit with accessories.

Single source system responsibility requires all major components to be supplied by a single source manufacturer.

©1992 ITT Corporation Printed in U.S.A. 11/92
Posted by permission from ITT Residential & Commercial Water Group
**NOTE: This article was originally published under the name ITT Fluid Handling. Where appropriate, the name has been edited to ITT Residential Commerical & Water Group, reflecting the current name of this subdivision of ITT Corporation.

Pump Start Up & Seal Failure

I’ve started my pump, and now it’s leaking . . .
Or even worse “I’ve started my pumps, and they are all leaking.” The next question is “when can this be fixed?” but the real question should be “why did the seal fail?” There are a variety conditions that can lead to seal failure, and the majority are preventable.

First, lets examine the conditions that are not preventable in the field. This could include a bad seal. It does happen, just not very often. Mean failure rates of the mechanical seals used in Bell & Gossett pumps are extremely low. Another possibility is an improperly constructed seal chamber in the pump itself. Out of thousands of pumps sold over the last few years, I am aware of one occasion wherein this was the case. While material failure is always a possibility, this is an extremely rare occurrence in our company’s experience.

The article will address typical start-up conditions and cleaning procedures for hydronic systems, basic water treatment of these systems, and the effect that the procedures and treatment will have on the pumps mechanical seals.

Start-up conditions, procedures and water treatment
Changes in new construction, particularly with regards to scheduling, have virtually guaranteed a pump seal failure soon after start-up. The rapid pace of new construction does not allow for use of flush pumps. Flush pumps require a pipe side stream with the appropriate valving to operate, and this does take time to construct and then remove. Please take a moment to consider when you last saw a flush pump being used on new construction, retrofit or T.I. work? When did you last see the use of a flush pump specified? In some informal surveying, five years was the most popular answer, and many people answered ten years.

This means that the system pumps have been used for conditions other than what they were designed for, namely system flush and cleaning. These conditions, and the accompanying fluid characteristics, present significant problems for pump seals.

To begin, one of the first things that will occur in a new system is a pressure test. Water is introduced into the system piping through the pump. This water is dirty, with high levels of sediment and construction debris, and is passed over the pump seal. This fluid contains high levels of dissolved and suspended solids. Mechanical seals are not tolerant of dissolved solid levels above 1000 ppm or suspended solids above 20 ppm, but we will address that in greater detail later.

System cleaning and pipe treatment are typically done with alkaline cleaners. Alkaline cleaning uses chemicals to raise the pH level in the system to somewhere between 9.5 and 10.5, with this level being most beneficial to the pipe.
A quick review of pH –

By definition pH is the measure of free hydrogen activity in water, and can be expressed as : pH = -log[H+]. A more practical statement for our purposes is that pH is the measure of acidity or alkalinity. Measured on a scale of 0-14, solutions with a pH of less than 7.0 are acids while solutions with a pH of greater than 7.0 are bases (alkaline). This is a logarithmic scale, and as such each unit represents a 10-fold increase or decrease relative to the next unit. For example, seawater with a pH of 8 is 10 times more alkaline than fresh, clean water, with a pH of 7. This is noted to illustrate how a pH increase or decrease of 1 or 1.5 is very significant with regards to the fluid properties.

Corrosion levels increase in copper and steel as pH falls below 7. This is acidic, and should make sense on an intuitive level. Since we don’t fill our systems with acids, this is a non-factor. Corrosion occurs readily at pH levels between 7 and 8.9, but falls off dramatically at 9, so the alkaline side of water treatment is where our attention should be focused.

The pH target is 9, with significant corrosion consequences if the system pH should fall below this number. As such, the most common treatment pH target range is between 9.5 and 10.5. Spikes in pH can occur, but for the most part this is not harmful to the piping. It can however be extremely harmful to the pump seal.

Mechanical Seal Tolerances
Internally flushed mechanical seals include a stationary face and a rotating element. The materials from which the seal are made have specific tolerance ranges with regards to temperature, pH and particulate levels. A standard seal, which will have carbon stationary element and a ceramic rotating element, has the following limitations:

· Maximum temperature: 225ºF
· pH range: 7 – 9
· Total dissolved solids: 1000 ppm
· Total suspended solids: 20 ppm

Based on what has already been outlined regarding start-up and water treatment, it can be reasonably assumed that the seals have already been subjected to conditions that exceed there limitations, and probably for an extended period. The water chemistry during cleaning will quite likely have a negative effect on the seal a few months later.

At elevated pH levels, the binder in the ceramic material is leached out, leaving the surface slightly softened and porous. As this element rotates, pieces of the ceramic embed in the carbon face and act like a grinding wheel on the weakened mating face. This will lead to seal leakage. Once the pH spike occurs, the damage is done regardless of subsequent adjustments.
The flushing water that cools and lubricates the seal evaporates due to the frictional heat generated between the seal faces, leaving behind whatever chemicals are dissolved in the water. For this reason, chemical concentrations of dissolved solids above 1000 ppm will act as an abrasive on the seal faces. This will erode the face, and the seal will leak. Similarly, with suspended solids, they can work between the faces and be trapped by the evaporation of the system fluid. The seal will be damaged as consequence.

If high pH levels and elevated concentrations of solids are typical of the installation, other seal materials are available as an option. Like anything, this will come at a price. These seals cost more, are more susceptible to thermal shock, and will crack quite readily if run dry even for a moment. The most common alternative seal would be of EPR/tungsten carbide construction. EPR, ethylene propylene rubber elastomer, is the stationary element. Tungsten carbide is the rotating element. This seal will tolerate pH levels of up to 11 and temperatures to 250ºF. Since the materials are harder, they will handle solids more effectively, but the exact amount is not published.

While we have not discussed temperature in depth, this is not typically an issue on standard hydronic heating systems, but may be a factor in some cogeneration facilities. Please bear in mind that at elevated temperatures, the effects of high pH levels become more pronounced, as well as the evaporation rate of the fluid between the seal faces. These seals will fail more rapidly as a result.

Conclusions and Solutions
How to cure the problem? The most cost effective solution is to simply change the seal after substantial completion of the project. While there are options regarding water treatment that will not elevate pH levels, they come at a steep price increase. Given our competitive market place, this is unlikely to be a regular alternative. Monitoring the water chemistry during start-up and system cleaning will provide an early indicator of seal replacement necessity. Please bear in mind that because the system is corrected does not mean that damage has not been done.

This is a topic about which very lengthy articles have been written, and it is impossible to discuss all the factors of seal failure at any length in this newsletter. I would welcome you comment and input on this topic.

by Mike Caffrey
Branch Manager - San Diego
Dawson Co.

References
· B&G Bulletin 4976 “Mechanical Seal Selection Guidelines”
· The Burgmann Dictionary at http://www.burgmann.com/
· The Chesterton web site at http://www.chesterton.com/
· John Crane Company, article “Avoiding Premature Seal Failure”

Thanks to Roy Ahlgren, Director of Training and Education, Bell & Gossett.
Thanks to Mark Pondel, Manager of Field Service, Bell & Gossett.
With Special Thanks to Michael Burns, General Manager, Aquatec.

Simple Yet Sophisticated

It isn’t often that a new product is introduced and one could argue that the method used in its development is far more interesting than the product itself. How many of us wish we were asked to give our input in the early design phase of the products we select and specify on a daily basis? For example, I just purchased a Toyota Sequoia and found that it really has some nice features, like both the driver and passenger front windows will automatically roll up or down when the driver’s side buttons are fully depressed. But does it make any sense that if my four year old wants the dome light on, I have to take my eyes off the road and reach behind my head and flip the switch with my hand? Every car I’ve ever owned had an easily accessible switch on the dash. I curse those Toyota engineers every time! Research and development is the basis for any new innovation that comes along, but how innovative can a good old fashion centrifugal pump be? Well, I can tell you that Bell & Gossett used some very simple-sophisticated techniques in the development of their new VSX double suction pumps.

They simply started their research by asking the customer what features and benefits were important to them. Utilizing a technique known as The Voice of the Customer, Bell & Gossett sent their centrifugal pump Product Line Manager, Steve Schmidt on an extensive information gathering assignment all over the country and the world for that matter.

Some of you might have even been part of the process about two years ago when Steve conducted in-depth interviews with more than 300 consulting/specifying engineers, contractors, building managers, wholesalers, distributors and other industry experts. He focused on learning about their business, their long and short term goals, and any problems or concerns that might have developed over the years. As a result, he did a lot of listening and little talking to flush out the true requirements of the customer, compiling a list of 600 legitimate "needs". Incredibly each "need" was listed on a "Post-It-Note" and displayed in his office where he could be constantly reminded of the task at hand. These "needs" were then broken down into groups and entered into an elaborate concept matrix that ranked the importance of each, in order to help with their implementation in the design phase of the project.

They sophisticatedly developed the new line of pumps by utilizing Computational Fluid Dynamics (CFD). In the past, pumps had been "improved" by either "tweaking" an existing impeller design or modifying the volute to enhance performance. Until now, a completely new double suction pump had not been developed by Bell & Gossett in over forty years. By implementing CFD technology, impellers were hydraulically matched with pump volutes, allowing pump engineers to concentrate on the desired "sweet spot" the pump curve was to incorporate.

Determining the curve’s "sweet spot" required taking a step back and looking at how pumps are being applied today and what prime movers are being offered in today’s market. Hydraulic targets were identified for several market applications and design parameters were then entered into the computer. This process was no simple task and required a bank of 18 computers working up to 30 hours to solve equations for just one set of hydraulics! During the course of the design process, liquid flow was electronically visualized and pressures generated along the pump surfaces were studied for optimization. When a design concept was narrowed down, and prior to moving to large scale CFD analyses, rapid prototype parts were created to either validate or disprove the computer model. Foam blocks of the pump parts were then created and served as stepping stones until a desirable design was finally developed.

The result of this tedious process is a product that will offer exceptional reliability and versatility to the HVAC industry. It truly is an exciting time to be associated with this industry. By the way, does anyone have Dr. Phil’s number? I’m really hung up on this dome light thing. HAPPY PUMPING!