Hydraulic Pumps and Valves

8/2/2019 Hydraulic Pumps and Valves

1/28


2/28

Pump characteristic

Operating pressure

Speeds

Displacement volume (V) volume of liquid per

revolution Volumetric flow rate: Q = n V

where n : number of rotation (rpm)

V : displacement volume (per rev)


3/28

Pump Efficiency (Volumetric)

To determine performance of pump

Divided into two:

Volumetric efficiency (vol): Indicates amount of

leakage that takes place in the pump. Effected bypressure.

vol = QA/QT

= (actual flow rate)/(theoretical flow rate)


4/28

Mechanical efficiency (m)Indicates amount of energy

losses due to reasons other than leakage.

m = pump output power(no leakage)/actual power delivered

to pump

=pQT/TAN

where p : pump discharge pressure [Pa]

QT: pump theoretical flow rate [m3/s]

TA : theoretical torque delivered to pump [Nm]

N : pump speed [rpm]


5/28

Or

m = TT/TA

= (theoretical torque to operate pump)/(actual torque

delivered to pump)

where TT[Nm] = (VD [m3] p [Pa])/2

TA = (actual power delivered to pump [W])/

(2N/60[rpm])


6/28

Total/overall efficiency

Total efficiency: tot= volm

where tot: total efficiencyvol: volumetric efficiency

m : mechanical/motor efficiency


7/28

Example (1)

A leakage of oil from a pump is 6% at 230 bar. Calculate thetotal efficiency if the flow rate at 0 bar is 10 dm3min-1 andthe motor efficiency is 75%.

Solution:

Q (P = 0 bar) = 10 dm3min-1

Q (P = 230 bar) = 10 0.94 = 9.4 dm3min-1

motor= 0.75,vol = 9.4/10 = 0.94

Therefore

tot = motorvol = 0.705 (= 70.5 %)


8/28

Example (2)

A pump has a displacement volume of 100 cm3. It delivers

0.0015 m3/s at 1000 rpm and 70 bars. The prime mover

input torque is 120 Nm.

a) What is the overall efficiency of the pump?

b) What is the theoretical torque required to operate the

pump?


9/28

Solution

a) From QT = V n,Given V = 100 cm3/rev

= 0.0001 m3/rev

QT

= V n

= 0.0001 m3/rev (1000/60 revs-1)

= 0.00167 m3/s


10/28

Solution Solve volumetric efficiency

vol = QA/QT

= 0.0015/0.00167 = 0.898 = 89.8%Solve mechanical efficiency

m = PQT/TAN

= (70 105)(0.00167)/(120)(1000 (2/60))

= 0.93 = 93%

Therefore, tot = 0.93 0.898 = 0.835 = 83.5%


11/28

Solution b) m = TT/TA

TT = m TA = 0.93 120 = 112 Nm


12/28

Assignment 3 The pump in Example 2 is driven by an electric motor

having an overall efficiency of 85%. The hydraulic system

operates 12 hours per day for 259 days per year. The cost

of electricity is RM0.11 per kWh. Determine:

a) The yearly cost of electric to operate the hydraulics

system.

b) Amount of yearly cost of electricity that is due to theinefficiencies of the electric motor and pump.


13/28


14/28


15/28

Basic valve symbols


16/28


17/28

1. Directional control valve Change, open or close flow path in hydraulic system.

Types:

1. 2 ports/2 way

2. 3 ports/2 way

3. 4 ports/2 way

4. 4 ports/3 way


18/28

2 ports/2 way valve 1 working port and 1 pressure port

Control delivery by closing or opening the passage


19/28

3 ports/2 way valve 1 working port, 1 pressure port and 1 tank

connection

Control deliveryo Normal position P is closed and A to T is open

o Actuated position T is closed, flow from P to A


20/28

4 ports/2 way valve 2 working port (A, B), 1 pressure port and 1 tank

connection

Control deliveryo Normal position flow from P to B and A to T

o Actuated position flow from P to A and B to T


21/28

4 ports/3 way valve


22/28

2. Non-return valves Allows hydraulic flow in only one direction.


23/28

3. Pressure valves Control and regulate pressure in a hydraulic system.

Types:

- Pressure relief valve- Pressure regulator


24/28

Pressure relief valve (PRV) To control and relieve pressure in a hydraulic system.

If the pressure generated exceeds the spring force,

the valve will open.

P

T


25/28

Pressure regulator Reduce the output pressure to safe/usable pressure.

Automatically shuts off hydraulic flow at a certain

pressure.

A

P T


26/28

4.Flow Control Valve Reduce the speed of cylinder or motor rpm

Eg - Throttle valve

o One way flow control valve


27/28

Throttle valve Used to restrict the flow from either direction

100%


28/28

One way flow control valve

Restrict the flow in one direction while allowing a bypass

in the opposite direction

Used to reduce the speed of cylinder movement

100%

Documents

Hydraulic Pumps and Valves