Download - Hydraulic Pumps and Valves
-
8/2/2019 Hydraulic Pumps and Valves
1/28
-
8/2/2019 Hydraulic Pumps and Valves
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)
-
8/2/2019 Hydraulic Pumps and Valves
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)
-
8/2/2019 Hydraulic Pumps and Valves
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]
-
8/2/2019 Hydraulic Pumps and Valves
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])
-
8/2/2019 Hydraulic Pumps and Valves
6/28
Total/overall efficiency
Total efficiency: tot= volm
where tot: total efficiencyvol: volumetric efficiency
m : mechanical/motor efficiency
-
8/2/2019 Hydraulic Pumps and Valves
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 %)
-
8/2/2019 Hydraulic Pumps and Valves
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?
-
8/2/2019 Hydraulic Pumps and Valves
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
-
8/2/2019 Hydraulic Pumps and Valves
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%
-
8/2/2019 Hydraulic Pumps and Valves
11/28
Solution b) m = TT/TA
TT = m TA = 0.93 120 = 112 Nm
-
8/2/2019 Hydraulic Pumps and Valves
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.
-
8/2/2019 Hydraulic Pumps and Valves
13/28
-
8/2/2019 Hydraulic Pumps and Valves
14/28
-
8/2/2019 Hydraulic Pumps and Valves
15/28
Basic valve symbols
-
8/2/2019 Hydraulic Pumps and Valves
16/28
-
8/2/2019 Hydraulic Pumps and Valves
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
-
8/2/2019 Hydraulic Pumps and Valves
18/28
2 ports/2 way valve 1 working port and 1 pressure port
Control delivery by closing or opening the passage
-
8/2/2019 Hydraulic Pumps and Valves
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
-
8/2/2019 Hydraulic Pumps and Valves
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
-
8/2/2019 Hydraulic Pumps and Valves
21/28
4 ports/3 way valve
-
8/2/2019 Hydraulic Pumps and Valves
22/28
2. Non-return valves Allows hydraulic flow in only one direction.
-
8/2/2019 Hydraulic Pumps and Valves
23/28
3. Pressure valves Control and regulate pressure in a hydraulic system.
Types:
- Pressure relief valve- Pressure regulator
-
8/2/2019 Hydraulic Pumps and Valves
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
-
8/2/2019 Hydraulic Pumps and Valves
25/28
Pressure regulator Reduce the output pressure to safe/usable pressure.
Automatically shuts off hydraulic flow at a certain
pressure.
A
P T
-
8/2/2019 Hydraulic Pumps and Valves
26/28
4.Flow Control Valve Reduce the speed of cylinder or motor rpm
Eg - Throttle valve
o One way flow control valve
-
8/2/2019 Hydraulic Pumps and Valves
27/28
Throttle valve Used to restrict the flow from either direction
100%
-
8/2/2019 Hydraulic Pumps and Valves
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%