Air Distribution

& Hydraulics Lecture - 5

VANEScrew

ReciprocatingScrew

Positive Displacement

Pumps and non PDP

PUMPS

Simplex & Duplex

Direct/Indirect acting

Simple gear pump Diaphragm

Pumping Theory difference between PDP and Dynamic (non PDP)

• A common application of pump that one can use in household where water is sucked with high suction capacity from the quite a depth and deliver to the top of the building. Here we use centrifugal pump, jet pump, submersible pumps & turbine pumps. These have high suction capabilities.

• In positive displacement pumps PDP, the liquid transferred from pumps suction side to its delivery in one revolution or cycle of operation of pump. The PDP we deliver liquids or oils from suction to delivery. And when liquid transferred to delivery one cant not get back then at suction side.

• The dynamic non PDP are in which turbine pumps, CF pumps, axial flow pumps, are at priority. In these pumps if delivery side is shut off by a valve the sucked fluid it will churn in side suction to delivery and vice versa. If PDP same thing is repeated by closing the delivery side shut off valve, the fixed volume rate of flow at the given speed of rotation the pump pressure will be continued to build up and would be a danger of pipe line burst off due to fluid pressure.

Positive Displacement Pump• A positive displacement pump is one in which a

definite volume of liquid is delivered for each cycle of pump operation. This volume is constant regardless of the resistance to flow offered by the system the pump is in,------------ provided the capacity of the power unit driving the pump or pump component strength limits are not exceeded

• The positive displacement pump differs from centrifugal pumps, which deliver a continuous flow for any given pump speed and discharge resistance.

• Positive displacement pumps can be grouped into three basic categories based on their design and operation. The three groups are reciprocating pumps, rotary pumps, and diaphragm pumps.

Reciprocating Pumps

• With a single suction port and a single discharge port as shown

• During the suction stroke, the piston moves to the left, causing the check valve in the suction line between the reservoir and the pump cylinder to open and admit water from the reservoir.

• During the discharge stroke, the piston moves to the right, seating the check valve in the suction line and opening the check valve in the discharge line.

Reciprocating Pumps

• Direct-acting • Indirect-acting • Simplex • Duplex • Single-acting • Double-acting • Power pump

Direct-Acting and Indirect-Acting Pumps

• Direct Acting pumps powered by a reciprocating steam piston. The piston rod of the steam piston may be directly connected to the rod of the piston of the pump or it may be indirectly connected with a beam or linkage

• Indirect-acting pumps are driven by means of a beam or linkage connected to and actuated by the power piston rod of a separate reciprocating engine.

Simplex and Duplex Pumps

• A simplex pump, sometimes referred to as a single pump, is a pump having a single liquid (pump) cylinder.

• A duplex pump is the equivalent of two simplex pumps placed side by side on the same foundation.

• Duplex is one piston type is on its upstroke the other piston is on its down stroke, and vice versa. This arrangement doubles the capacity of the duplex pump compared to a simplex pump of comparable design

Single-Acting and Double-Acting Pumps

• A single-acting pump is one that takes a suction, filling the pump cylinder on the stroke in only one direction, called the suction stroke, and then forces the liquid out of the cylinder on the return stroke, called the discharge stroke.

• A double-acting pump is one that, as it fills one end of the liquid cylinder, is discharging liquid from the other end of the cylinder

Non PDP or

Dynamic

non PDP or Propeller Design Pump• Most hydraulic pumps are positive-

displacement (PDP) devices • PDP have higher efficiencies than their

non- PDP counterparts, such as impeller or centrifugal designs

• non-PDP designs that could be used to run hydraulic circuits. Because these pumps only run at 50 to 75% efficiency, they are not used in high-pressure circuits.

• They are frequently found in systems with high-water-content fluids (HWCF), such as 95% water and 5% soluble oil,

• These pumps require little or no lubrication.

• These systems usually operate at or below 400 psi.

• Some PDP are paired with centrifugal pumps to pressurize their inlets to keep them from cavitations.

• Or when a PDP is run at higher rpm than specified, the inlet may not be large enough to let in enough fluid at

• , atmospheric pressure. In this case a non-PDP can force fluid into the undersized inlet and eliminate cavitations.

• A non-PDP does not require a relief valve in many installations. There is enough slippage in most designs to allow for stopping flow while not over pressuring the circuit.

Positive Displacement Pump (PDP)

• PDP have two types • 1. Rotary• 2. Reciprocating• PDP have two types from construction point

• 1. Based on delivery of oil Flow------------1. Fixed Displacement

• 2. Based on Construction 2. Variable Displacement

• i. Gear Pump---------Fixed Displacement

• ii. Vane Pump---------Fixed and Variable

• iii. Axial Piston Pumps-------- Variable Displacement

• vi. Radial Piston Pumps-------Variable Displacement

Rotary Pumps• Rotary pumps operate on the principle that a rotating

vane, screw, or gear traps the liquid in the suction side of the pump casing and forces it to the discharge side of the casing.

• There are many types of positive displacement rotary pumps, and they are normally grouped into three basic categories that include

• Gear pumps,• Screw pumps, • Moving vane pumps.

• Clearances between rotating parts, and between rotating and stationary parts, be kept to a minimum in order to reduce slippage. Slippage is leakage of fluid from the discharge of the pump back to its suction.

• Due to the close clearances in rotary pumps, it is necessary to operate these pumps at relatively low speed in order to secure reliable operation and maintain pump capacity over an extended period of time. Otherwise, the erosive action due to the high velocities of the liquid passing through the narrow clearance spaces would soon cause excessive wear and increased clearances, resulting in slippage.similar to duplex double-acting steam pumps,

Gear pumps Rotary

• Rotary are relatively expensive pumps and can rarely be justified on the basis of efficiency over centrifugal pumps. However, they are frequently justified over steam reciprocating pumps where continuous duty service is needed due to the high steam requirements of direct-acting steam pumps

• In general, the effective flow rate of reciprocating pumps decreases as the viscosity of the fluid being pumped increases because the speed of the pump must be reduced.

• In contrast to centrifugal pumps, the differential pressure generated by reciprocating pumps is independent of fluid density. It is dependent entirely on the amount of force exerted on the piston

Comparison of Reciprocating, Rotary, CF

pumps

Simple Gear Pump•

There are several variations of gear pumps. The simple gear pump consists of two spur gears meshing together and revolving in opposite directions within a casing. Only a few thousandths of an inch clearance exists between the case and the gear faces and teeth extremities. Any liquid that fills the space bounded by two successive gear teeth and the case must follow along with the teeth as they revolve. When the gear teeth mesh with the teeth of the other gear, the space between the teeth is reduced, and the entrapped liquid is forced out the pump discharge pipe.

• With the large number of teeth usually employed on the gears, the discharge is relatively smooth and continuous, with small quantities of liquid being delivered to the discharge line in rapid succession

• In all simple gear pumps, power is applied to the shaft of one of the gears, which transmits power to the driven gear through their meshing teeth.

There are no valves in the gear pump to cause friction losses as in the reciprocating pump.

• In Centrifugal pumps high impeller velocities, with resultant friction losses, are not in simple gear pumps.

Gear Pump

Other Gear Pumps

• There are two types of gears used in gear pumps in addition to the simple spur gear. One type is the helical gear. A helix is the curve produced when a straight line moves up or down the surface of a cylinder.

• The other type is the herringbone gear. A herringbone gear is composed of two helixes spiraling in different directions from the center of the gear. The herringbone gear pump is also a modification of the simple gear pump.

• Its principal difference in operation from the simple spur gear pump is that the pointed center section of the space between two teeth begins discharging before the divergent outer ends of the preceding space complete discharging.

• This overlapping tends to provide a steadier discharge pressure. The power transmission from the driving to the driven gear is also smoother and quieter

pointed center section

Lobe type pump• The lobe type pump is another variation of the

simple gear pump. It is considered as a simple gear pump having only two or three teeth per rotor; otherwise, its operation or the explanation of the function of its parts is no different.

• Some designs of lobe pumps are fitted with replaceable gibs, that is, thin plates carried in grooves at the extremity of each lobe where theymake contact with the casing. The gib promotes tightness and absorbs radial wear.

Lobe Pump

Screw pumps Positive Displacement Rotary Pump

Two-Screw, Low-Pitch, Screw Pump Three-Screw, High-Pitch, Screw Pump

Screw pumps

Oil Pump Screw PumpMarine double screw pump

Capacity: 0.5-1500m3/h Pressure: 0.1-2.0Mpa Viscosity: 0.5-100, 00mm2/s Temperature: -30 - 200 C Medium: Various lubricating oil and fuel oil

Capacity: 0.5-1500m3/h Pressure: 0.1-2.0Mpa( For gas and oil mixture pump, the pressure is 0.1-4 Mpa)

Viscosity: 0.5-100, 00mm2/s Temperature: -30 - 200 C Medium: Various lubricating oil and fuel oil

Screw Pump

Screw Pump

• These pumps are also known as positive-displacement pumps. It is also probably the world's oldest type of pump. Recently, it has become accepted in the United States for general use in pumping wastewater.

• It was based on the Archimedes screw principle that has a revolving shaft fitted with one, two, or three helical blades to rotate in an inclined trough and push the wastewater up the trough.

• This type of pump has two very evident advantages over the afore-mentioned centrifugal pumps,

• (1) it can pump large solids without clumping, (2) it operates at a constant speed over a wide range of flows with good efficiencies.

Blacksburg Wastewater Treatment Plant (SCREW PUMP)

Moving Vane pumps Vane compressor

Pumping Chamber

Cam ring Surface

Vane compressor

VANE

Slots

Vane Pump

Rotary Moving Vane Pump

• The rotary moving vane pump is another type of positive displacement pump used. The inner rotating element causes liquid to be pumped out.

• In C.F pump it the rotation of the impeller.• In Vane pump we have cylindrical rotor that has grooves or slots along

the circumference that has housed a number of vanes . The vanes have loose fit in side the slots.

• The ring of the cam is elliptical shape.• Rotor with the vane are known as cartridge unit. The cartridge units are

splined on to the driving shaft. A cam ring is fitted inside the pumping chamber of splined shaft. As the driving shaft rotates the vanes come out of the slots due to centrifugal action.

• The design of the cam ring and the rotor does not allow them to come out completely.

• The rotor moves with 600 rpm.• The continuous contact of the vane tip and the ring of cam wear out their

surface. The manufactures of vane pump offers cartridge for the replacement .

• The increase and decrease in flow rate is also possible by changing a different cartridge kit of cam ring and vanes.

23 Liter per sec

22 1800rpm

21

20

19

18

17 1500rpm

16

15

14

13 1200rpm

12

11 1000rpm

10

09

10 KW

09 input

08 power

07

06

05

04

03

02

01

0

Vane pump performance characteristic Curve

35 70 105 140 175 210

PRESSURE in bars

Vane pump curve characteristics• Another way to increase the flow rate is to increase the

speed of the vane pump motor• The decline in rate of speed will increase the working

pressure • In the graph when Pump pressure is 70 bars at 1500rpm

the discharge is 17 l/ mint and the Kilo watt energy is required about 7 kw

• The pump KW can be calculated by PQ/600 approximately Kilo watts

• If flow rate is cc/ rev we can multiply cc with rpm and divide by 1000 to get liters/ mint, so we have Q= Lit/mit

• We have rpm in 1000, 1500 and 3000 which are always shown as 960 1440 and 2880 etc.

• P is in bars or psi. If bars to convert in psi just multiply with 14.5psi with bars and get P=psi

Example to convert 200bars in

to psi.• If 1bar= 105 Pa;• 1 bar= 14.5 psi; ---------1 Pascal =0.000145 psi then

200bars = 105 x 200 Pascal• 200bars = 105 x 200 (1 Pascal)

200 bars =105 x200 (0.000145 = 2900psi)• SIMPLE If 14.5x 200 we get = 2900 psi

• To get KW we use P*Q/600 = Lbs / in2 x liters /sec /550 ft Lbs /sec

• =( Lbs/in2) xLs/sec x(103/ 2.543 )x(1/12)x (sec / 550 x ft Lbs) x746

• = wattsx1000 kw

Diaphragm pumps

• Diaphragm pumps are also classified as positive displacement pumps because the diaphragm acts as a limited displacement piston. The pump will function when a diaphragm is forced into reciprocating motion by mechanical linkage, compressed air, or fluid from a pulsating, external source. The pump construction eliminates any contact between the liquid being pumped and the source of energy. This eliminates the possibility of leakage, which is important when handling toxic or very expensive liquids.

• Disadvantages include limited head and capacity range, and the necessity of check valves in the suction and discharge nozzles.

Scroll Pump