Session 9 Pumps and pump design

TOTAL TIME: 1 to 2 Hours

OBJECTIVES: To investigate pump design by reviewing a variety of pumps

To learn the basic operating principles common to all displacement pumps

MATERIALS: Blackboard or equivalent

Drawings of pumps or actual pumps and pump components (old and new if possible)

PROCEDURES:

Step 1: 30 minutes

Begin by discussing the pump design shown in the accompanying attachments. Discuss the various methods for attaching the pump to the mill and the necessity of securing the sections of sucker rod firmly together. Explain the construction and use of swivels and crossheads.

Trainer Note

Either examples or models of the things you are talking about are invaluable here. Have good flipchart-sized drawings of the things of which you do not have any hardware samples.

Step 2: 15 minutes

Extract from the examples the minimum parts common to the displacement type pump-inlet valve, outlet valve, something to displace the water.

Trainer Note

If building a pump is part of the training, then have a finished example of that pump available for inspection.

Step 3: 15 minutes

Discuss the difference between a pump that works submerged in water (borehole type) and a pump that works above the water level and must suck water up to it. Note the approximately 20 foot (7 meter) limit in height the pump can be located above the water level for the non-submersible pump.

Trainer Note

If the training is done at high altitudes, the height a lift pump can draw water decreases. The decrease is at the rate of 1 meter per 1000 meters (3300 ft) of elevation above sea level.

RESOURCES:
Copies of "Rules of Thumb for Wind Waterpumps"
Session 7 (Attachment 7-A)
Copies of Attachment 9-A

Attachment 9-A

Figure 1: "Hand Pump" with Single-acting, Bucket-piston

Figure 2: Persian Wheel with Portgarland Drive Wheel and Horizontal Drive Shaft

Figure 3: Square Wooden Piston-type Water Pump

Figure 4: Double-acting Piston-type Water Pump

Figure 5: Wooden-pallet-type Water Pump

Figure 6: Steel-washer Chain-type Water Pump

Figure 7: Square Wooden Enclosed Chain-type Water Pump

Figure 8: Centrifugal Reaction-type Water Pump

Figure 9: Large-diameter Slow-speed Centrifugal-type Water Pump

Figure 10: Netherlands "Tjasker" - type Rotor and Water Pump

Figure 11: Peristaltic-type Water Pump

Attachment 9-A

MISCELLANEOUS PUMPS

1. Reciprocating Pumps

Most reciprocating pumps have the disadvantage that the torque lead is not constant, thus requiring a higher wind velocity for starting, and variable stresses on the system when in operation.

(a) The single-acting cylindrical piston pump is most frequently used in wind-powered pumping systems. It consists of a cylinder with an inlet pipe and valve at the base, a leather-sealed piston with a one-way valve and a water outlet at the top, water passing through the pump only on the lifting stroked of the piston. This type of pump is used to pump water from any depth, with an operating speed of up to 40 strokes per minute.

(b) A square wooden single-acting piston pump is commonly used by fishermen in eastern Canada (figure 3) and has recently been adapted to wind power. A square wooden pump powered by the wind has been powered for use in Thailand. The height of lift is limited by the amount of water pressure that can be sustained by the wooden joints, although the simple construction is well adapted to basic carpentering skills.

(c) The double-acting piston pump (figure 4) is similar to the single-acting pump, except that there is no valve or passage of water through the piston, the water by-passing the piston cylinder through pipes and valves under pressure during both the upstroke and the downstroke. The advantage of this pump over the single-acting pump is that the load of the power source is more constant, but it is not usually used in wind pumping systems because any compression load during the downstroke could buckle the long piston rod leading from the top of the tower; this problem could be avoided if a very short piston rod were connected to an immediately adjacent rotary power transfer mechanism powered by a long belt leading directly from the rotor shaft.

(d) The diaphragm pump (figure 4) consists of a cylinder closed tat the lower end, with a circular diaphragm of rubber or some other material fixed at the top end. A reciprocating connecting rod is fixed to the center of the diaphragm and, upon vertical movement causes volumetric displacement in the cylinder. An arrangement of valves allows water movement in only one direction through the cylinder. The difficulty with this pump is the high rate of wear on the diaphragm at its connection with the cylinder and connecting rod. A diaphragm pump has been developed for use with a Savonius rotor.

(e) The inertia pump (figure 3) is a very simple and efficient device that depends upon the vertical inertia of a body of water in a reciprocating pipe to expel water at the end of the upstroke of the pipe. A one-way flap valve in the pipe is closed during the upstroke, and inertia is imparted to a fresh volume of water by the lifting force on the pipe. This pump must operate at a constant frequency which is dependent upon the mass of water in the pipe and the pipe itself. This recently popularized pump has probably not yet been used with wind power.

2. Rotary-Motion Pumps

Continuous rotary-motion pumps are well adapted to operation by wind power because they require a constant torque load and generally operate at a variable low speed.

(a) The square-wooden-pallet chain pump (figure 5) is commonly used in China and southeast Asia for lifts up to 3m and consists of rectangular wooden pallets or paddles mounted on a continuous wooden chain that runs up an inclined square-section open wooden trough. The paddles and chain pass around a large wooden driving gear wheel at the top and around a small passive gear wheel at the base of the trough which is submerged in water. This type of pump is commonly used with Chinese vertical-axis wind pumping systems and with Thai high-speed wooden rotors and Thai sail rotors.

(b) The round-steel-washer chain pump (figure 6) is used in conjunction with human and animal power and consists of a continuous steel chain upon which are mounted steel discs with rubber or leather washers. The chain passes around an upper gear wheel, down the well, under the water source, around and then up into the bottom of a pipe with inner diameter the same as the washers. Water is lifted up within the pipe and expelled at the top. A square wooden adaptation of this pump is shown in figure 7.

(c) Large-diameter slow-speed centrifugal pumps (figure 8) have good potential for low-lift pumping. The meadow type wind pump of the Netherlands are fitted with centrifugal pumps 1m in diameter and 0.2m high, with four wooden blades, and have an efficiency of 30 per cent and an output of up to 100 m³ per hour in a strong wind. Further design development and quantification of design variables of these pumps could be undertaken.

Another type of centrifugal pump is the centrifugal reaction pump (figure 9) which consists of a vertical pipe with a T-joint at the top, from which extent two pipes whose length is dependent upon the rate of rotation of the assembly in operation. An orifice at the end of each pipe arm points 90° away from the arm. When the assembly is filled with water and rotated in the direction opposite to the orifices, the water is forced out through the orifices by centrifugal force and replenished by water coming up through a valve in the bottom of the vertical pipe. This pump is well adapted to variable low speeds, and construction is simple. One of these pumps, connected to a 3m diameter high-speed wind rotor, pumped 30 m³ per hour at a head of 4.5m in a 29 km/in wind.

(d) Axial-flow pumps have good potential for low-lift pumping because. of their relatively simple construction and high efficiency. No use of these pumps with wind rotors is recorded, but it has been suggested that axial-flow pumps would be appropriate for high-volume pumping of sewage wastes in oxidation ponds. Theoretical studies of wind-powered axial-flow pumps are being carried out at the National Aeronautical Laboratory in India.

(e) Archimedian screws are very simple and have efficiencies up to 80 percent. They have been used in the Netherlands for large-scale drainage requiring a lift of up to Sm. Three basic versions are known:

(i) The type with a rotating cylinder made of strips of wood and having a spiral partition inside (figure 10), as in the Tjasker type of wind pump in the Netherlands, requires a footstep bearing below the water level, and demands a fairly sophisticated level of construction skill. It can be made large in diameter and so suitable for slow-speed operation. Such a screw, 2.7m long, 0.56m diameter and lifting through 1.3m at a speed of about 30 rev/mint gives an output of 32.4 m³ per hour.

(ii) The type in which the outer casing is stationary and the helical rotor is supported on bearings at either end, attached to the casing, are normally of smaller diameter and run at a high speed, e.g. 12-cm diameter up to 200 rev/min, 40-cm diameter up to 127 rev/mint An advantage of this type is that the casing and rotor form a self-contained assembly which does not require external bearings but only simple supports to maintain it at the correct angle and axial position. The screw is made by rolling a flat steel strip between rollers set at an inclination to each other to squeeze one edge of the strip and hence cause it to curl into a helix, which is then welded to an inner cylindrical pipe.

(iii) A third method of constructing an Archimedian screw is to coil a section of pipe into a cylindrical helix. A particular type has recently been evolved for field drainage in which the tubing is corrugated with a fine pitch to strengthen it and to allow coiling to a small radius. This could form the basis of a simple low-cost pump, since most of the construction could be done locally. For example, a stout bamboo could serve as the main axle, and the coil of pipe could be held in place by lashing with rope, wire, or any suitable local fibre, using longitudinal strips of bamboo or other wood to form a supporting cage on the inside of the coils.

(f) The peristaltic pump (figure 11) consists of a flexible hose with a series of rollers along the length of the hose in order to squeeze water through the hose. The type of pump has reportedly been adapted to a Greek sail wind rotor at the Malaysian Agricultural Research and Development Institute.