Archive for January, 2011

Three Piece Booster Pumps

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The three-piece booster pump illustrated in Figures 10-11 and 10-12 is an example of the circulators used in small-to medium-size residential and light commercial hydronic heating systems since the 1930s.

A typical three-piece booster pump consists of the following three sections: (1) the pump body (also called the volute, body assembly, or waterway), (2) the coupling assembly, and (3) the motor assembly (also called the shaft-and-motor assembly).

three piece booster pump Three Piece Booster Pumps

The three-piece booster pump contains hermetically sealed sleeve bearings, a carbon/ceramic seal, and a coupler that uses springs in tension to provide quiet operation. The motor of a three-piece booster pump can be serviced by removing it from the pump body. Consequently, there is no need to drain the system or disconnect the pump from the piping for servicing.

three piece booster pump cross sectional Three Piece Booster Pumps

The three-piece booster pump has an inline volute, which means the inlet and discharge ports are located along the same centerline. It has a strong starting torque, which enables it to free a stuck impeller without any difficulty.

The volute is just another term for the pump body. It contains the motor bracket, the impeller, the volute gasket, the inlet and discharge ports, and the pump mounting flanges.The shape of the volute will determine how the circulator is connected to the piping.

A three-piece booster pump requires periodic inspection. The mechanical seal will sometimes need replacement. After removing the old seal, clean the shaft and sleeve before installing a new one. The pump manufacturer will provide step-by-step instructions for servicing the pump mode.

This pump also requires periodic lubrication. A wool wicking is used to draw the lubricating oil into the bearing assembly (see Figure 10-13). Check the pump manufacturer’ s operating and maintenance instructions for the recommended lubricating schedule. As shown in Figure 10-13, the three-piece booster pump must always be installed with the oil ports facing upward and with the motor, motor shaft, and bearing assembly in a horizontal position.

series 100 booster pump Three Piece Booster Pumps

Never plug or cover the weep hole, or you will trap the excess oil in the pump body.Any dirt or sediments in the oil may damage the bearings and shorten their service life.

Use only the lubricant specified by the pump manufacturer. An SAE 20 (nondetergent) or 10W-30–weight oil can be substituted if the pump manufacturer’s recommended oil is unknown.

The three-piece booster pump shown in Figures 10-11 and 10-12 can be installed to discharge in any direction (e.g., up, down, horizontally, etc.), but the motor shaft must always be in the horizontal position, the arrow on the pump body must always point in the direction of flow, and the conduit box must be positioned on top of the motor housing.

Water Circulating Pumps

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Hydronic heating systems use small compact pumps to provide the motive force to circulate the water in the pipes. They are usually referred to as circulators or water-circulating pumps. The circulator is used to move the water from the boiler to the heat-emitting units and back again. It is not used for lifting, as is the case with vacuum and condensate pumps, but simply for circulating the water through a closed loop.

Circulators were first introduced in the 1930s to augment water circulation in the traditional hot-water space-heating systems. Prior to their introduction, the hot-water systems relied on the density difference between cold and hot water to provide the motive force for water circulation. These systems were called gravity hot-water heating systems, and the pumps were added to boost circulation. These early pumps (sometimes called three-piece circulators or booster pumps) are still with us today, although as more technically advanced models. All modern hydronic heating systems are closed loop installations that use one of several different types of pumps to circulate the water.

Vacuum Pumps

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Vacuum heating pumps are used to maintain the vacuum in mechanical vacuum heating systems by removing air, vapor, and condensation from the lines. Many vacuum pumps are available in both single and duplex units, and are designed to automatically adjust themselves to the varying conditions of the system. The duplex units have an advantage over the single pumps, because they provide automatic standby service. If one of the pumps in a duplex unit should happen to malfunction, the other one cuts in and picks up the load.

A vacuum pump is operated either by steam or electricity. Steamdriven vacuum pumps are sometimes used in high-pressure steam systems, but these pumps have been generally replaced by automatic motor-driven return-line pumps. Examples of vacuum heating pumps are shown in Figures 10-7 and 10-8.

return line vacuum pump Vacuum Pumps

In operation, the pump is started before the steam enters the system. When the pump removes the air from the lines, steam quickly fills the radiators of the system. The radiators remain full of steam, because the air is automatically removed as fast as it accumulates. By quickly exhausting the air and condensation from the system, the vacuum pump causes the steam to circulate more rapidly, resulting in faster warm-up time and quieter operation.

duplex return line vacuum pump Vacuum Pumps

The condensation of steam in the lines creates the vacuum, and the pump maintains it by continuing to pump air from the system. The vacuum maintained by the pump is only a partial one, because it is not possible with this device to extract all the air. Each stroke of the pump piston or plunger removes only a fraction of the air, depending on the percentage of clearance in the pump cylinder, the resistance of valves, and other factors; hence, an infinite number of strokes would theoretically be necessary to obtain a perfect vacuum, not considering line and pump resistance.

Vacuum pumps designed to remove only air from a system are referred to as dry pumps. Those that remove both air and condensation are called wet pumps. When a wet pump is used, the condensation is pumped back to the boiler. In operation, the air, being heavier than steam, passes off through thermostatic retainer valves to the pump. When the steam reaches the retainer valves, they close automatically to prevent the steam passing into the dry return line to the pump and breaking the vacuum. The air from the pump is passed into a receiver, where it is discharged through an air vent. The condensation is pumped back to the boiler generally by means of a centrifugal pump.

In most vacuum systems, the pump is controlled by a vacuum regulator and a float control. The vacuum regulator cuts in when the vacuum drops to a preset level and cuts out when the vacuum reaches its highest point. The float control operates independently from the vacuum regulator, starting the pump when condensation reaches a certain level in the receiver.

Two typical installations in which vacuum heating pumps are used are illustrated in Figures 10-9 and 10-10. In the vacuum air-line heating system, shown in Figure 10-10, thermostatic-type air-line valves are used instead of radiator air vents. The primary purpose of the vacuum heating pump is to expel air from the system.

vacuum pump two pipe heating system Vacuum Pumps

The vacuum return-line system is very similar to a condensation return steam heating system, except that a vacuum pump is used to provide a low vacuum in the pipes and to return the condensation to the boiler. Because of the vacuum condition, smaller steam traps and piping can be used.

vacuum pump two pipe heating system with accumulator Vacuum Pumps

An accumulator tank must be installed in a vacuum pump steam heating system if the returns are below the inlet connection of the vacuum pump receiver. As shown in Figure 10-10, the condensate flows by gravity from the baseboard heating units to the accumulator tank, where it is lifted to the vacuum pump receiver.

Condensate Pumps

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The design of a conventional gravity-flow steam heating system is such that the heat-emitting units cannot be placed at a level lower than the water level in the boiler. The movement of the condensation depends on gravity and, therefore, must move from a higher to a lower level until it reaches the boiler (at the lowest level). This is illustrated by the one-pipe steam heating system in Figure 10-1. Each heating unit has a single pipe through which it receives the hot steam and returns the condensate in the opposite direction. The dependence on gravity to return the condensate to the boiler places certain limitations on the design of the heating system unless mechanical means are used to compensate for the lack of gravity. A condensate pump serves this purpose.

one pipe heating system Condensate Pumps

Many different types of condensate pumps have been developed for use in steam heating systems. Screw, rotary, turbine, reciprocating, and centrifugal pumps are some of the types used for this purpose. One of the most common uses of condensate pumps in low-pressure steam heating systems is the motor-driven centrifugal pump equipped with receiver (tank) and float-control automatic switch.

In operation, condensation enters the receiver and fills the tank. A float connected to an automatic switch rises with the water until the tank is almost full. At that point, the float closes the switch and starts the pump motor. The water is pumped from the receiver and the float drops, causing the switch to open and shut off the pump motor.

The centrifugal pump shown in Figure 10-2 is used to pump condensation from a lower level return line to one at a higher level, or against a higher pressure. These units are also used to pump condensation from a flash tank to a boiler (see Figure 10-3) and for other special applications.

centrifugal condensate pump Condensate Pumps

pumping condensation Condensate Pumps

As shown in Figure 10-4, the basic components of this pump consist of an impeller (A), with an inlet at its center rotating on a shaft (D). The condensation enters the inlet orifice and flows radially through vanes to the outer periphery (F) of the impeller; it has approximately the same velocity as the periphery. The head of pressure developed by the pump is the result of the velocity imparted to the condensation by the rotating impeller.

centrifugal condensate pump components Condensate Pumps

When the condensation leaves the outer periphery of the impeller, it flows around the volute casing (B) and through the discharge orifice (E) of the pump. A wear ring (C) is provided to prevent bypassing of the condensation.

Condensate pumps are available in either single or duplex units. The latter are used in installations where it is necessary to have a pump available for use at all times. A duplex unit is actually two condensation pumps fitted with a mechanical alternator. Both pumps feed into the same receiver. If one pump malfunctions, the other starts automatically and continues to provide uninterrupted pumping service for the system.

Vertical condensation pumps are available for use in installations where the space for the pump is limited, where the returns run below the floor, or where it is undesirable to place a horizontal pump in a sunken area. Vertical condensation pumps are also available in both single and duplex units.

The use of a condensate pump in a two-pipe steam heating system is shown in Figure 10-5. Note the arrangement of gate and check valves on the discharge side of the pump. This type of system is commonly referred to as a condensate-return steam heating system. Using a condensate pump to return the condensation provides greater design flexibility for the system. The major disadvantage is that larger steam traps and piping must be used than in vacuum heating systems.

condensate pump two pipe heating Condensate Pumps

Condensate pumps can also be used as mechanical lifts in vacuum steam heating systems (see Figure 10-6). By connecting the vent outlet of the condensation pump to a return line above the level of the vacuum heating pump, the same vacuum return condition is maintained in the piping below the water level as in the rest of the system. In this arrangement, the only purpose of the condensate pump is to lift the condensation from the lower level to the higher one without reducing the capacity of the vacuum heating pump.

condensate pump mechanical lift Condensate Pumps

Steam and Hydronic System Pumps

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Heating and circulating pumps are used to maintain the desired flow rate of steam or hot water in a heating system.

The two types of pumps used in steam heating systems are (1) condensate pumps and (2) vacuum heating pumps. The condensate pump is used in a gravity steam heating system to return the condensation to low- or medium-pressure boilers. Vacuum heating pumps are used in either return-line or variable-vacuum heating systems to return condensation to the boiler and to produce a vacuum in the system by removing air and vapor along with the condensation.

Circulators are used in hot-water (hydronic) heating systems to maintain a continuous flow of the water in the system. They are smaller in size than either a condensate or a vacuum pump and are usually of the motor-driven centrifugal type.

Socket-Welding Procedure

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The procedure for making a socket weld is as follows:

1. Cut the pipe end square, making sure the diameter is not undersize or out of round.
2. Remove all burrs with a metal file.
3. Clean the pipe end, valve joint, and the inside of the valve socket with a degreasing agent to remove any oil, grease, or other foreign material.
4. Insert the pipe end into the valve socket and space by backing off the pipe after it hits against the shoulder inside the spacing collar. Tack weld in place.
5. Make certain the valve is in the open position before applying heat. Valve bonnets should be hand-tight to prevent distortion or damage to the threads. Nonmetallic discs should be removed before applying heat.
6. The valve and pipe should be supported during the welding process and must not be strained while cooling.
7. Preheat the welding area 400°F to 500°F .
8. A socket weld can generally be completed in two to four passes, depending on the welding method used. Make sure the first pass is clean and free from cracks before proceeding with the second pass. Avoid excessive heat because it may cause distortion to the valve bonnet.
9. Use a wire brush and a clean cloth to remove discoloration.

Butt-Welding Procedure

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The procedure for making a butt weld is as follows:

1. Machine the pipe ends for the butt-welding joint.
2. Clean the pipe ends, valve joint, and the inside of the valve socket with a degreasing agent to remove oil, grease, or other foreign materials.
3. Align by means of fixtures, and tack weld in place.
4. Make certain the valve is in the open position before applying heat. The valve bonnet should be hand-tight to prevent distortion or damage to the threads. Nonmetallic discs should be removed before applying heat.
5. The valve and pipe should be supported during the welding process and must not be strained while cooling.
6. Preheat the welding area 400°F to 500°F .
7. Depending on the welding method used (gas, arc, and so on), a butt weld is normally completed in two to four passes. The first pass should have complete joint penetration and be flush with the internal bore of the pipe. Make sure the first pass is clean and free from cracks before proceeding with the second pass. The second pass should blend smoothly with the base metal and be flush with the external diameter. Avoid excessive heat because this can cause distortion and possible malfunctioning of the valve.
8. Use a wire brush and a clean cloth to remove discoloration.

Soldering or Silver-Brazing Procedure

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The basic procedure for soldering or silver-brazing pipe or tubing to valves is as follows:

1. Cut the tube or pipe end square, and make sure the diameter is not undersize or out of round.
2. Remove all burrs with a metal file.
3. Clean the pipe or tubing end (at least to the depth of the socket) and the inside of the valve socket with steel wool and
a cloth to wipe away the residue.
4. Clean all surfaces with a suitable solvent and wipe dry.
5. Apply solder flux or silver-brazing flux to the inside of the valve socket and the outside of the pipe or tubing.
6. Insert the pipe or tubing into the valve socket until it seats against the shoulder within the socket.
7. Turn the valve and the pipe or tubing once or twice to evenly distribute the flux.
8. Make certain the valve is in open position before applying heat. A nonmetallic disc should be removed before the heat is applied. After removing the disc, the valve bonnet or bonnet ring should be replaced hand-tight to prevent distortion to the threaded sections when heating the valve.
9. Make certain the valve and pipe or tubing are properly supported during the soldering or silver-brazing process. Any strain on the joint while cooling will weaken it.
10. Apply flame evenly around piping or tubing adjacent to valve ends until solder or brazing alloy suitable for the service flows upon contact.
11. Soldering: Apply solder to the joint between the pipe or tubing and the end of the valve socket. Apply the flame toward the bottom of the valve socket until all the solder is absorbed. Control the direction of the flame away from the valve body to avoid excessive heating, which causes distortion and improper functioning of the valve.
12. Silver brazing: Apply brazing alloy to the joint between the pipe or tubing and the end of the valve socket. Wave the flame over the valve hexes to draw the metal alloy into the socket, leaving a solid fillet of brazing alloy at the joint. Control the direction of the flame away from the valve body to avoid excessive heating, which causes distortion and improper functioning of the valve.
13. Remove all excess and loose matter from the surface with a clean cloth or brush.

Valve Installing Pointers

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Unless valves are installed properly, they will not operate efficiently and can cause problems in the system. There are certain precautions you should take when installing valves that will improve their performance and minimize the possibilities of a malfunction. These precautions may be summarized as follows:

1. Always clean out a valve before installation because dirt, metal chips, and other foreign matter can foul it. This can be done by flushing the valve with water or blowing it out with compressed air.
2. Clean the piping before installing the valve. If you cannot flush or blow out the foreign matter, the ends of the pipes
should be swabbed with a damp cloth.
3. Only apply paint, grease, or joint sealing compound to the pipe threads (that is, the male threads). Never apply these
substances to the valve body threads because you run the risk of their getting into the valve itself and interfering with its operation.

4. Install valves in a location that can be reached conveniently (see Figure 9-47). If the valve is placed so that it is awkward to reach, it sometimes may not be closed tightly enough. This can eventually cause leaks to develop in the valve.

valve installation Valve Installing Pointers

5. When necessary, support the piping so that additional strain is not placed on the valve. Small or medium-size valves can be supported with hangers placed on either side. Large valves should always be independently suspended.

6. Sufficient clearance is particularly important when rising stem valves are used. Failure to ensure proper clearance
before installing the valve may cause damage to the disc sealing surface.

Damaged Valve Stems

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Sometimes the threads on valve stems become worn or damaged, making the valves inoperable. When this occurs, the stems must be replaced. Before the stem can be replaced, however, all pressure must be removed. Then, with pressure removed, disconnect and remove the bonnet and upper valve assembly. The remainder of the procedure depends on the type of stem used (that is, rising or nonrising stem) and other design factors. Basically, the procedure may be summarized as follows:

1. Run the stem down by turning it in a clockwise direction.
2. Rotate the stem in a clockwise direction until the stem threads are completely out of the threaded portion of the upper bushing.
3. Pull the stem out of the stuffing box.
4. Remove the wedge or disc from the stem.
5. Replace the old stem with a new one.
6. Reassemble in reverse order with new packing and gasket (when applicable).