6.
Review of hydraulic principles
Tool circuit
6.1.
Hydraulic formulas
Example: HP required to deliver 10 GPM at 1500 PSI.
Estimated HP delivered by pump or used by tool
6.2. Back pressure
Back pressure measured at the tool return port must not exceed the manufacturers back pressure rating. Most
manufacturers list the maximum back pressure for their hydraulic tools at 250 PSI. Back pressure measured on
the return side of the tool is the force required to get the oil back to the tank. In almost all cases the lower the back
pressure the better the tool performance. First, the back pressure is subtracted from the maximum tool pressure
to arrive at a maximum tool operating pressure. For example, tools with 2000 PSI operating pressure are installed
on a system with 250 PSI back pressure. This leaves 1750 PSI as a maximum tool pressure. Imagine a system
with 500 PSI back pressure. 2000 Minus 500 PSI back pressure leaves only 1500 PSI for the tool. Second, tools
are designed for pressure to build on the pressure side of the tool. If too much pressure builds on the return side,
not only is performance effected, but seals may blow. This is why it is very important to direct the flow into the tool
correctly. Reversing the hoses to test may result in blown seals, damage to the tool, and personal injury.
PSI
GPM
500
1000
1500
2000
2500
3000
3
1.03
2.06
3.09
4.12
5.15
6.18
5
1.72
3.43
5.15
6.86
8.58
10.30
10
3.43
6.86
10.30
13.70
17.20
20.60
15
5.15
10.30
15.40
20.60
25.70
30.90
10 av 26
OPERATION AND MAINTENANCE MANUAL I ENG_OMM_BRIDGE_SPREADER_P01 I 02th December 2021
@Pandrol 2021
