Piston Pump

A piston pump contains an accurately machined ceramic or stainless-steel piston moving in a cylinder normally fitted with double ball inlet and outlet valves.

From: Principles of Fermentation Technology (Third Edition), 2017

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Hydraulic Pumps and Pressure Regulation

Andrew Parr MSc, CEng, MIEE, MInstMC, in Hydraulics and Pneumatics (Third Edition), 2011

Piston pumps

A piston pump is superficially similar to a motor car engine, and a simple single cylinder arrangement was shown earlier in Figure 2.2b. Such a simple pump, however, delivering a single pulse of fluid per revolution, generates unacceptably large pressure pulses into the system. Practical piston pumps therefore employ multiple cylinders and pistons to smooth out fluid delivery, and much ingenuity goes into designing multicylinder pumps which are surprisingly compact.

The displacement of a piston pump can be easily calculated:

Q=(number of pistons)×(piston area)×(piston stroke)×(drive speed)

Figure 2.12 shows one form of radial piston pump. The pump consists of several hollow pistons inside a stationary cylinder block. Each piston has spring-loaded inlet and outlet valves. As the inner cam rotates, fluid is transferred relatively smoothly from inlet port to the outlet port.

Figure 2.12. Radial piston pump

The pump of Figure 2.13 uses the same principle, but employs a stationary cam and a rotating cylinder block. This arrangement does not require multiple inlet and outlet valves and is consequently simpler, more reliable, and cheaper. Not surprisingly most radial piston pumps have this construction. Like gear and vane pumps, radial piston pumps can provide increased displacement by the use of multiple assemblies driven from a common shaft.

Figure 2.13. Piston pump with stationary cam and rotating block

An alternative form of piston pump is the axial design of Figure 2.14, where multiple pistons are arranged in a rotating cylinder. The pistons are stroked by a fixed angled plate called the swash plate. Each piston can be kept in contact with the swash plate by springs or by a rotating shoe plate linked to the swash plate.

Figure 2.14. Axial pump with swash plate

Pump displacement is controlled by altering the angle of the swash plate; the larger the angle, the greater the displacement. With the swash plate vertical displacement is zero, and flow can even be reversed. Swash plate angle (and hence pump displacement) can easily be controlled remotely with the addition of a separate hydraulic cylinder.

An alternative form of axial piston pump is the bent axis pump of Figure 2.15. Stroking of the pistons is achieved because of the angle between the drive shaft and the rotating cylinder block. Pump displacement can be adjusted by altering the drive shaft angle.

Figure 2.15. Bent axis pump

Piston pumps have very high volumetric efficiency (over 98%) and can be used at the highest hydraulic pressures. They are, though, bulky and noisy. Being more complex than vane and gear pumps, they are correspondingly more expensive and maintenance requires more skill. Table 2.1 gives a comparison of the various types of pump.

Table 2.1. Comparison of hydraulic pump types

Type Maximum pressure (bar) Maximum flow (l min–1) Variable displacement Positive displacement
Centrifugal 20 3000 No No
Gear 200 375 No Yes
Vane 200 400 Yes Yes
Axial piston (swash plate) 350 750 Yes Yes
Axial piston (valved) 500 1500 Yes Yes
In-line piston 1000 100 Yes Yes

The figures in Table 2.1 are typical values and manufacturers’ catalogs should be checked for a specific application. The displacement of gear, vane and radial piston pumps can be increased with multiple assemblies. Specialist pumps are available for pressures up to about 7000 bar at low flows. The delivery from centrifugal and gear pumps can be made variable by changing the speed of the pump motor with a variable frequency (VF) drive.

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Dynamic modelling and design of bent axis pumps

Mohammad Suliman Abuhaiba, in Positive Displacement Machines, 2019

Description of bent axis piston pump/motor

Piston pumps provide the greatest ranges of overall performance. They can be driven at high speeds to provide a high power-to-weight ratio. They can operate at pressure levels in excess of 5000 psi. Due to very close-fitting pistons, they have the highest volumetric efficiencies (Esposito, 2003).

Fig. 1 shows a schematic bent axial piston pump that contains a barrel with pistons rotating with the main shaft. The centreline of the barrel is set at an offset angle relative to the centreline of the main shaft. The barrel contains a number of pistons arranged along a circle. The piston connecting rods are attached on the main shaft base plate by ball and socket joints. The pistons are forced in and out of their bores as the distance between the main shaft base plate and barrel edge changes. A constant velocity joint connects the barrel to the main shaft to provide synchronous movement of the barrel.

Fig. 1. Basic components of a bent axis pump (Abuhaiba, 2009).

The operation of the pump begins with a torque imposed on the main shaft. This torque causes rotation of all elements ending in the barrel, which is allowed to rotate within the yoke of the pump. The centre shaft of the barrel is fixed to the yoke, which is nonrotating about the centreline of the main shaft. The yoke is allowed to rotate around an axis perpendicular to the main shaft. If the yoke is set to an angle other than zero, the pistons on a fixed length connecting rod reciprocate in the cylinders as the distance between the edge of the barrel and the base plate shortens and lengthens as the main shaft rotates. Low-pressure oil on the suction side is drawn into the cylinder through a valve as the piston retracts in the cylinder. In order to ensure the availability of oil at the suction port and to avoid cavitation, the low-pressure side is often pressurized to a modest pressure. As the piston starts to ride up the cylinder, the oil is injected into the high-pressure discharge port.

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Fluid Dynamics

NICOLAE CRACIUNOIU, BOGDAN O. CIOCIRLAN, in Mechanical Engineer's Handbook, 2001

2.8.4 AXIAL PISTON PUMP

An axial piston pump is shown in Fig. 2.25. The major components are the swashplate, the axial pistons with shoes, the cylinder barrel, the shoeplate, the shoeplate bias spring, and the port plate. The shoeplate and the shoeplate bias spring hold the pistons against the swashplate, which is held stationary while the cylinder barrel is rotated by the prime mover. The cylinder, the shoeplate, and the bias spring rotate with the input shaft, thus forcing the pistons to move back and forth in their respective cylinders in the cylinder barrel. The input and output flows are separated by the stationary port plate with its kidney-shaped ports. Output volume may be controlled by changing the angle of the swashplate. As angle a between the normal to the swashplate and the axis of the drive shaft in Fig. 2.26b goes to zero, the flow volume decreases. If angle a increases (Fig. 2.26a), the volume also increases. Axial piston pumps with this feature are known as overcenter axial piston pumps.

Figure 2.25. Axial piston pump. (a) Overcenter axial pump without drive shaft shown. (b) Basic parts for axial piston pump.

Figure 2.26. Simplified schematic of the operation of the compensator piston in controlling the angle of the swashplate to control output flow rate. (a) Large displacement for full flow. (b) Zero displacement for no flow.

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HYDRAULIC PUMPING

James F. Lea, ... Mike R. Wells, in Gas Well Deliquification (Second Edition), 2008

9.3.1 Operation

Hydraulic subsurface piston pumps are composed of two basic sections—a hydraulic engine and a piston pump. They are directly connected with a middle rod. As the engine piston moves upward, the pump piston also moves upward, causing the barrel chamber under the pump piston to fill with production fluid. When the hydraulic engine makes a downstroke, the pump piston also makes a downstroke, displacing the production fluid in the pump barrel.

The arrangement of the pump end is the same as with a sucker rod pump in that there is a barrel, a piston, a piston traveling valve, and a standing valve. Since there is no mechanical linkage to the surface because the sucker rod string is replaced by a column of high pressure power fluid, many limitations of sucker rod pumping are eliminated.

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DESIGN OF WATER PUMPING WITH SOLAR ARRAY FIELD

H. KULUNK, in Energy and the Environment, 1990

SOLAR PUMPING SYSTEM

Urfa which is placed at the south-east part of Turkey is suffered from lack of insufficient water for irrigation and relatively less developed part of Turkey. However, Urfa experiences very high solar radiation throughout the whole year as presented on Table 1 (Kiliç et al., 1983). One of the challenge of people in Turkey is at least to double current production of food. The achievement of this national goal requires appropriate management of land as well as sufficient water resources. Solar irrigation system suits very well to Urfa. In this work, representation of solar pumping project and determination of system characteristics are studied step by step.

Table 1. Monthly average of daily solar radiation (MJ/m2.day) and sunshine (hr/day) at slope 40 degrees for Urfa (kiliç et al., 1983).

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Radiation 10.1 12.8 15.5 18.2 20.4 21.5 21.9 22.1 21.0 18.1 13.6 10.2
Sunshine 4.2 5.1 6.1 7.9 10.6 12.6 12.8 11.9 10.3 8.4 6.2 4.6

Pump Characteristics

Immersible piston pump of type Jacuzzi SJI-D 10 and DC motor system are utilized in this investigation. Characteristic curves of pump and motor are taken from literature (Acar, 1988) and shown on Fig. 1.

Fig. 1. Characteristics of pump Jacuzzi SJI-D 10 and DC motor (Acar, 1988).

Amount of Water Pumped

Daily water pumped Q(kg/day) is computed by the formula proposed by Lysen (1983)

(1)Q=Qm(I−Io)/(Im−Io),

where Qm(kg/day) and Im(MJ/m2.day) denote maximum daily water pumped and daily radiation respectively. In equation (1), I =5 MJ/m2.day and represents threshold daily radiation at which system starts pumping and I(MJ/m2. day) denotes daily radiation. For a reasonable flow rate of 0.6 k6/s one can easily determine Qm, using Table 1, as

Qm0.6(kg/s)×11.9×3600(s/day)=25704 kg/day.

Hence by known values of Im =22.1 MJ/m2.day we can calculate daily and monthly pumped water. Results of computations are presented on Fig. 2.

Fig. 2. Distribution of amount of water pumped monthly for Urfa, according to equation (1).

Total Pumping Head

Total pumping head H(m) is sum of static and dynamic heads. For flow rate of 0.6 kg/s and total pumping head of 15m and using Fig. 1., one can find: pump poower P=200 W, DC motor voltage=30 V and pump efficiency=44 %. Details of pumping heads are shown explicitly on Fig. 3. Since corresponding water flow velocity for a pipe of diameter d=0.0254m is V=1.19m/s, Reynoulds number (Re) then becomes

Fig. 3. Water pumping system and pumping heads.

Re=1.19(m/s)×0.0254(m)/10−6(m2/s)=3×104,

which implies turbulance flow. From Fig. 3., total static head is 10+7-4=13m while total dynamic head Hd(m) is only 2m as calculated by

(2)Hd=(V2/2g)+(λ×L/d)×(V2/2g),

where g=9.8m/s2, λ and L denote frictional constant and pipe length respectively. λ is determined usually from Moody diagrams. Using Moody diagrams (Giles, 1962) one finds λ=0.03 and with L=23m from Fig. 3., consequently determines dynamic head as 2m. PVC water tank of capacity 10m3 is sufficient for the present system.

Daily Electrical Energy Demand (DEED)

Daily Electrical Energy Demand is computed by

(3)DEED(Whr/day)=P(W)×Daily Sunshine(hr/day).

Corrected value of DEED is calculated by DEED/0.85. For example, for January, using Table 1, one gets DEED=200(W)×4.2(hr/day)=840Whr/day and corrected DEED as 840/0.85=988 Whr/day. Using PV module of type BP-A-1233 (16.2V; 2.05A peak or 33W peak), the corrected daily solar panel energy supply is found as 33(W)×4.2(hr/day)×0.85=117.8Whr/day and so number of module is found as 988/117.8=8.39. However, due to under estimated values, number of modules is accepted as 10. Number of modules is 30V/16.2V=1.85 or roughly 2, hence number of row of modules is 10/2=5. This situation is shown on Fig. 4.

Fig. 4. PV array field to power 30V DC motor.

Efficiency Computations

System efficiency ηs and peak panel efficiency ηp can found by

(4)ηs=Q×g×H/n×A×I,
(5)ηp=Panel Peak Power(W)/Ic×A,

where n is number of solar module, A(m2) is total solar cell area per module (about 41 % of module is cell area for BP-A-1233) and IC is peak solar radiation usually taken as 1000w/m2. For January Q=7666kg/day, I=10.1×106 J/m2.day and with g=9.8m/s2, H=15m, ηn = 6.1% and ηn = 18.2 %.

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Sampling

J.G. Giles, in Instrumentation Reference Book (Fourth Edition), 2010

Rotary Pumps

Rotary pumps can be divided into two categories, the rotary piston and the rotating fan types, but the latter is very rarely used as a sampling pump.

The rotary piston pump is manufactured in two configurations. The Rootes type has two pistons of equal size which rotate inside a housing with the synchronizing carried out by external gears. The rotary vane type is similar to those used extensively as vacuum pumps. The Rootes type is ideal where very large flow rates are required and, because there is a clearance between the pistons and the housing, it is possible to operate them on very dirty gases.

The main disadvantage of the rotary vane type is that, because there is contact between the vanes and the housing, lubrication is usually required, and this may interfere with the analysis.

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HYDRAULIC PUMPS

R. Keith Mobley, in Fluid Power Dynamics, 2000

Swash Plate Design Pumps

In axial piston pumps, the cylinder block and drive shaft are on the same centerline and the pistons reciprocate parallel to the drive shaft. The simplest type of axial piston pump is the swash plate inline design (Figure 3-15).

Figure 3-15. Inline design piston pump.

The cylinder blow in this pump is turned by the drive shaft. Pistons fitted to bores in the cylinder are connected through piston shoes and a retracting ring, so that the shoes bear against an angled swash plate. As the block turns (Figure 3-16), the piston shoes follow the swash plate, causing the pistons to reciprocate. The ports are arranged in the valve plate so that the pistons pass the inlet as they are being pulled out and pass the outlet as they are being forced forward.

Figure 3-16. Swash plate causes pistons to reciprocate.

In these pumps the size and number of pistons as well as their stroke length also determine the displacement. The stroke length is controlled by the swash plate angle. In variable-displacement models, the swash plate is installed in a movable yoke (Figure 3-17). By pivoting the yoke on pintles, the swash plate angle and piston stroke can be increased or decreased. Figure 3-17 shows a compensator control, but the angle can also be controlled manually or by a variety of other means.

Figure 3-17. Pressure compensator control.

Operation of the inline compensator-controlled pump is shown schematically in Figure 3-17. The control consists of a compensator valve balanced between load pressure and the force of a spring, a piston controlled by the valve to move the yoke, and a yoke return spring. With no outlet pressure, the yoke return spring moves the yoke to the full-delivery position. As pressure builds, it acts against the end of the valve spool. When the pressure is high enough to overcome the valve spring, the spool is displaced and oil enters the yoke piston. The piston is forced by the oil under pressure to decrease the pump displacement. If the pressure falls off, the spool automatically moves back, oil is discharged from the piston to the inside of the pump casing, and the spring returns the yoke to a greater angle.

The compensator adjusts the pump outlet to whatever displacement is required to develop and maintain the preset pressure. This prevents excess power loss by avoiding relief valve operation at full pump volume in holding and clamping applications.

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Casting

John Campbell, in Complete Casting Handbook (Second Edition), 2015

Direct-acting piston displacement pump

Direct-acting piston pumps for lead and zinc appear to be successful. However, their attempted use for liquid Al alloys has so far not resulted in success. Although such wear-resistant and Al-resistant materials as SiC can be finely and accurately ground to make cylinders and pistons, the damage caused by particles of alumina ensures that the pumps quickly wear and fail. Sweeney (1964) describes how attempts to produce cylinder and piston pumps were rapidly abandoned because of oxide problems. Valves such as the ball check type similarly proved unreliable because of oxides. Such failure is hardly surprising. Films of alumina of thickness measured in nanometres will probably always be present in alloys of liquid Al, and will easily find their way into the most accurately fitting parts, leading inevitably to scoring and wear.

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Casting manufacture

John Campbell OBE FREng DEng PhD MMet MA, in Complete Casting Handbook, 2011

Direct-acting piston displacement pump

Direct-acting piston pumps for lead and zinc appear to be successful. However, their attempted use for liquid Al alloys has so far not resulted in success. Although such wear-resistant and Al-resistant materials as SiC can be finely and accurately ground to make cylinders and pistons, the disruption caused by particles of alumina ensures that the pumps quickly wear and fail. Sweeney (1964) describes how attempts to produce cylinder and piston pumps were rapidly abandoned because of oxide problems. Valves such as the ball check type similarly proved unreliable because of oxides. Such failure is hardly surprising. Films of alumina of thickness measured in nanometers will probably always be present in alloys of liquid Al, and will easily find their way into the most accurately fitting parts, leading inevitably to scoring and wear.

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Glycol Maintenance, Care, and Troubleshooting

Maurice Stewart, Ken Arnold, in Gas Dehydration Field Manual, 2011

Insufficient Glycol Circulation

If there is insufficient glycol circulation, check heat exchangers and glycol piping for restrictions or plugging.

On an electric driven piston pump:

Check flow rate indicator (if present) to insure proper glycol circulation. If flow rate indicator is not present, verify circulation rate by closing the glycol discharge valve from the contactor and timing the fill rate in the gauge column.

Check high-pressure dry-glycol bypass valve. Close if necessary.

Check pump prime by shutting pump down, closing the discharge valve, opening the bypass valve and restarting the pump. Allow to run briefly under no load through the bypass line to remove any trapped gas in the pump.

On glycol-gas powered pumps:

Close dry discharge valve. If pump continues to run, open dry discharge bleed valve and allow to run a few strokes. Once all gas is purged from put, close the bleed valve. If pump continues to run, discontinue use and send in for repair.

If pump will not prime, but continues to run gas through the dry discharge bleed valve then:

Check pump suction strainer for plugging.

Check glycol level in surge tank.

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