Gate valves are rather simple valves that should be used as only open/close valves. Media such as steam going through the gate of the valve not fully open will cause a restriction through the valve thus increasing the velocity of the steam going through the valve which will eventually cut through the valve’s “gate” and render the valve useless.

Gate valves are classified as a rising stem or a non-rising stem valve. A rising stem gate valve will give the plant operator visual reference if the valve is open or closed.

Gate valves generally are threaded or flanged and are manufactured in bronze, stainless, iron, and a variety of other metals and pressure ratings.

As with any mechanical valve, careful consideration of application should be exercised on selecting the proper valve.

Once again Thank You Process Technology for the excellent video.

If you are in the Maryland, Virgina, or southern Pennsylvania area, M & M Controls is the “go-to” controls company for all your boiler and building automation control needs. In my interview with Pat Marsala, the founder and president of M & M Controls,
we explore what a full service controls distributor looks like. Learn about M & M Controls Systems Integrator and Control Integrator programs and benefit from the insights of one of the HVAC controls industries most knowledgeable individuals. Pat and his team at M & M controls are members of Controls Group North America. With their large inventory of Honeywell, Johnson Controls, Fireye, Belimo, Siemens, Functional Devices, McDonnell & Miller and a top notch team of controls experts, M & M Controls receives a thumbs up rating for Controltrends as a reliable and trusted Controls Distributor.

Next time you are in the Baltimore area be sure to stop in and see Pat and his team.

Excellent video for those domestic boiler installations. Stromquist and Company have the parts you need to keep those boilers running properly. Give us a call at 1-800-241-9471

In this power point presentation, compliments of Greg Towsley and slide share check, out what you need to know about boiler feed water control.

I have been asked over the years “What is a boiler horsepower” and what is the design criterion of square feet of heating surface per boiler horsepower.

 To understand boiler horsepower it is necessary to review the genesis of the term “boiler horsepower” (Bhp). The term originally related to the quantity of steam necessary to operate a one horsepower steam engine. Due to variations in engine efficiencies, this quantity of steam was itself a variable. Tests conducted in 1876 on a modern (for the time) steam engine determined that it took approximately 30 pounds of steam per hour to produce 1 horsepower (mechanical) of work. In 1889 the American Society of Mechanical Engineers (ASME) standardized the term “Boiler Horsepower” as being based on a conventional steam engine steam rate of 30 pounds of steam per hour (PPH) at 70-psig pressure and feedwater of 100 degrees F. This definition was later modified to: “Boiler Horsepower = the unit of capacity expressed as equivalent evaporation of 34.5 pounds of water per hour from and at 212 degrees F (33,475 Btu per hour.)”

In the early days of brick firing surfaces the rule of thumb was that it took 10 square feet of heating surface to create 1 boiler horsepower. In todays modern boiler designs the heating surface necessary to create 1 boiler horsepower has been reduced to 5 or in some cases less that 5 square feet of heating surface.

HORSEPOWER ?

As we all know before machines we did all the heavy work… then “Joe” one day hitched a horse to a rock to move the rock. Without knowing it at the time “Joe” created the term motive power. Motive power is a term used to describe something (air, water, steam, or the horse) that has the energy (power) to create movement in something else. So, as steam engines replaced the horse as a means of motive power steam engines were were rated in horsepower instead of “Joe Power”. Sorry Joe !

Hope you enjoy this bit of horsepower history.

We have written many articles about flame safe guard controls on Control Trends but we have not really given an explanation on the basic principles of these controls.

The programmer, (also called the blue box, the FSG, the fire eye and the brain) is the mastermind that controls the starting sequence and the firing cycle of a burner. The programmer controls the operating sequence of the blower, burner motor, ignition system, fuel valve, and all other components also called interlocks in the control system.

The programmer also provides, if necessary, a suitable purge period before ignition and after burner shut down allowing for the removal of explosive combustibles. The programmer is designed to de-energize all fuel valves within 4 seconds after loss of flame signal. In addition, the programmer automatically restarts a new cycle each time a temperature controller or pressure controller closes or after a power failure, lock outs must be reset manually after any flame failure.

Example of basic operation of programmer on steam boiler:

When the steam pressure within the boiler drops the pressure controller, (like Honeywell L404F1102), completes an electric circuit which starts a timing sequence in the programmer. The first timing sequence closes and starts the burner motor that rotates the primary air fan. The primary air fan blows air into the furnace to purge any unburned fuel present in a gaseous condition in the furnace.

This process is called pre-purging the furnace. By pre-purging the furnace before pilot ignition, the danger of a furnace explosion is reduced. The purge cycle is controlled by the time card (ST7800) in most programmers and can last varying lengths of time depending on the furnace size.

The programmer is still operating and when the second timing sequence contact closes, the circuit to the ignition transformer (similar to Donagan AO6-SA) is completed. The ignition transformer creates a high voltage spark in front of the gas pilot tube. At the same time, a solenoid valve is opened in the gas pilot line, allowing the gas to flow through the gas pilot tube and be ignited by the transformer spark. The scanner ( like the C7027A1023 or similar) is located on the front of the boiler and positioned in such a manner to sight the flame from ignition.

Sighting the pilot through the will verify that the pilot is lit. This process is called proving the pilot. The programmer timing sequence is still operating and the next contact closes to complete the circuit to the main fuel valve, which opens only when the scanner proved pilot. The main fuel valve is then opened and the fuel enters the furnace and is ignited by the pilot.

The programmer continues to operate for a few more seconds, securing circuits to the ignition transformer and the gas pilot. After the circuits are secure the programmer stops. The burner is now regulated by the pressure control and modulating pressure control. If the scanner senses a flame failure, the system is purged and secured. The programmer is then manually reset to restart the cycle.

The programmer needs very little maintenance. Most common failures are due to heat and moisture causing corrosion to the contacts of the programmer. Care must be taken to eliminate these factors. Check all wiring to the programmer sub-base for loose damaged connections or cracked wiring.

NOTES:

Please be aware this is a GENERIC ARTICLE on the workings of a burner programmer. There are MANY variations of these controls and many applications using these controls. Extreme care must be exercised when working with FSG CONTROLLERS and refer to factory and manufacture’s guides when working with these controls.

When your needs turn to the flame safe guard control please give Stromquist and Company at call at 1-800-241-9471.

I know that many of us are visual learners so I was able to locate these videos on fire tube boilers for part 2, as a compliment to my earlier post on The Principles of Fire Tube Boilers Part 1. Enjoy.

For replacement controls for your Fire tube boilers including Honeywell Flame safeguard Controls like the Honeywell Delphi Boiler Control System contact one of the control pros at Stromquist & Company if you are located in Georgia or Florida or one of our affiliates at Controls Group North America if you are located in another part of the country.

Stromquist and Company does not sell fire tube boilers but we do sell a vast amount of controls for these boilers from manufactures such as Conbraco, Honeywell, Asco, McDonnell & Miller, Maxitrol, and numerous other control manufacturers. The understanding of these boilers is a major concern in our continuing efforts to keep our readers informed.

FIRE TUBE BOILERS:

In a fire tube steam boiler, heat and gases of combustion pass through the tube surrounded by water. Fire tube boilers steam boilers maybe either high or low pressure boilers. The three types of fire tube steam boilers are horizontal return tubular boiler, scotch marine boiler, and vertical fire tube boiler.

All fire tube boilers have the same basic operating principles. The heat produced by the gases of combustion pass through the tubes while the water surrounds the tubes. However, fire tube boilers have different designs like 2 pass, 3 pass, and 4 pass based on application and installation considerations.

Fire tube boiler tubes are always measured by their outside diameter (O.D.). Fire tube boilers are usually designed for pressures up to a maximum of 250 psi and approximately 750 horsepower.

HOW THEY WORK:

When water is heated, it increases in volume and becomes lighter. This warmer water, now lighter, rises and the cooler water drops to take its place. The steam bubbles that eventually form break the surface of the water and enter the steam space.

The addition of tubes inside the drum containing the water increases the heating surface. The heating surface is that part of the boiler with water on one side and the heat and gases of combustion on the other. By increasing the heating surface, more heat is taken from the gases of combustion. This results in a more rapid water circulation and faster formation of steam bubbles.

When larger quantities of steam are released, the thermal efficiency of the boiler increases. Thermal efficiency is the ratio of the heat supplied from the fuel to the heat absorbed by the water. Modern fire tube boilers with improved design and heat transfer rates have achieved thermal efficiency rates as high as 80% to 85%.

Placing an internal furnace within the boiler shell greatly increases the heating surface allowing for maximum absorption of heat thus reducing the time to create steam.

BOILER SAFETY:

Because of the large volume of water fire tube boiler contain, disastrous explosions may occur. Explosions may occur because of a sudden drop in pressure without a corresponding drop in temperature. Knowledge of basic principles of boiler operation can prevent serious accidents.

Water will boil and turn into steam when it reaches 212 degrees F at atmospheric pressure.

The higher the steam pressure, the higher the boiling point of the water in the boiler.

As steam pressure in the boiler increases, there is a corresponding increase in temperature.

When a steam boiler is operating at 100 psi gauge pressure the temperature of the water and steam will be about 337 degrees F. If there is a sudden drop in pressure from 100 psi to 0 psi without a corresponding drop in temperature, the water at 337 degrees F flashes into steam. When water flashes into steam its volume increases tremendously. This can result in a disastrous explosion.

It is imperative that maximum care is exercised in the operation and maintenance of the fire tube boiler. This includes annual boiler inspections of the waterside and fireside of the boiler. Controls such as the low water cut off, relief valves, flame safeguards must all be in correct working order.

Proper boiler blowdown is an essential part of firetube boiler operating proceedures. It is necessary to control the amount of TDS (total dissolved solids) in the boiler water.The total TDS should not exceed 3500 parts per million in a scotch marine boiler. If the blowdown is not controlled, excessive dissolved solids will have a tendency to increase and concentrate to a point that will cause a foaming or a carry over condition which will contaminate the  steam.

High concentrations of TDS in firetube boilers have a tendency to collect as SCALE on the heat transfer surface. Scale is an excellent insulator and its collection on the heat transfer surfaces of a boiler reduces the efficiency of the boiler. Scale thickness between 1/50 of an inch to 1/9 of an inch depending on the type of carbonates or sulfates present can reduce boiler efficiency between 3.5% to 16%. As you can tell just a small amount of scale build up can cost thousands of dollars a year on fuel costs.

Boiler blowdown frequency and duration is recommended by the water treatment contractor and can be accomplished either manually or automatically or both. Manual blowdown involves the operating personnel opening the boiler blowdown valves for a predetermined length of time at proper intervals. Automatic blowdown can be accomplished by many means. The most common method is the use of a surface blowdown skimmer attached to a calibrated blowdown valve which permits a continuous preset amount of boiler water to be blown down.

Proper blowdown rate can be easily figured when two factors are known. It is necessary to know the TDS in the feedwater and the amount of makeup water the boiler is using. The amount of TDS in the feedwater can be determined from a water analysis. The quantity of make up water is determined by installing a water meter in the make up water supply line that serves the feedwater unit. The correct amount of boiler blowdown, as a percentage of feedwater can be figured with the following formula.

TDS in feedwater / 3500-TDS in feedwater X 100. For example if the TDS in the feedwater = 200 divide this by 3500-200 or (3300) the result is .06 the multiply .06 X 100 for the amout of 6% of makeup water for proper boiler blowdown. I hope this is clear as the mud you will now be removing from your boilers.

NOTE: Because of the many variations of boiler plants, boiler, valves, pumping systems, and control systems proper maintenance of these systems should follow manufacturer’s recommendations and federal, state, and local laws that govern these proceedures. Boilers and Boiler maintenance can be dangerous and should only be preformed by Boiler professionals that have the proper training. When in doubt defer to the Boiler manufacturer.

The following is a list of what causes a LWCO switch to malfunction taken from the McDonnell & Miller Service Guide.

   1. Burner motor having greater power requirements than the LWCO switch

   2. Feed pump is not properly balanced for the required fill rate resulting in rapid cycling of the switches.

   3. Shorting of power wiring in control circuit.

   4. Switch submerged in water

   5. Lightning striking electrical service to building, causing electrical overload

   6. Overloaded circuit in building, resulting in low voltage conditions which in turn causes higher amperage draw and consequent switch failure

   7. Other limits like pressure controls, relays, thermostats, etc., may short circuit, overloading all switches in the same electrical line.

   Pump motor having a dead spot, may stall and generates heat, causing overloading of switch

The most common cause of switch overload is incorrect application. Check the electrical ratings of the switch against ratings of the equipment controlled.

If ypu have any other questions about McDonnell & Miller controls please call Stromquist at 1-800-241-9471 in Atlanta or 1-800-678-7828