Calgary, Alberta, Canada dzyanis@engineer.com

Fluid Power Pro

Gear flow divider pressure

One product I’m working on has a gear type flow divider. This is a unit with mechanically linked four gear motors:

Today was asked the question: what happen if some of the lines be broken or leaking:

Somebody who is not familiar good enough with hydraulics can be confusing to know that the pressure at the actuator can be increased in this case. Moreover, the in this case the flow divider will work as a pressure multiplication device.

Why?

The answer we can get if research this device from the point of power transfer.


Assume, we have the inlet pressure 2000 PSI and the supplied flow at 12 GPM. The value of flow at each outlet port is proportionally gear motor displacement. In our case the flow divider has the same displacement in each gear motor, so outlet flow is: 12 GPM / 4 = 3 GPM:

 

Ok, but what about the pressure?

The inlet power is 14 HP:

\frac{P_{IN} \cdot Q_{IN}}{1714}=\frac{2000 PSI \cdot 12 GPM}{1714} = 14 HP

The outlet power will be divided between 3 loaded ports: 14 HP / 3 HP = 4.67 HP:

So, the pressure at each outlet port is:

P_{OUT} = \frac{HP \cdot 1714}{Q_{OUT}} = \frac{4.67 \cdot 1714}{3} = 2.666 PSI

If two outlets are without load, the pressure in loaded ports will be 4000 PSI:

If three outlets are without load, the pressure in the loaded port will be 8000 PSI (!!!):

This is why each gear-type flow divider has pressure relief valves inside, to prevent pressure issues, adjusted at max work pressure:

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