problem operating 2 geared motors at the same time with one hyd pump

Question

problem operating 2 geared motors at the same time with one hyd pump

ozzy3406 (Mechanical)

(OP)

17 Apr 10 02:15

i installed one hydraulic pump fixed displacement 25 gal/min.two motor spool v20 sectional valve bank .the motors must run independently w flow controles. the lift motor is rated at 16 gpm has 1" ports and 1/2"case drain.the flowcontrole for this motor has 3 3/4" ports.
the shaker motor rated at 6 gal/min has 3/4"ports and the flow controle has 3 1/2" ports.
the problem im having is when i run the two motors at the same time the shaker motor works great on #3 on flowcontrole however the lift motor runs les than half even with the flow control on all the wayand heres the wierd thing when i turn up the shaker motor the lift motor goes faster too. am i just missing something here?
any help would be greatly apreciated.

hydtools (Mechanical) · Answer 1 · 2010-04-17 08:50:44

You are using bypassing flow controls.  When the shaker motor control is set to low flow excess flow from the fixed displacement pump is being dumped back to tank and little flow is avaialble for the lift motor.
When you increase the flow to the shaker motor the pressure rises also pushing more flow to the lift motor.
Where are the flow controls in the circuit?  Before or after the directional valves?
You would be better off with a tandem pump.  One side for the shaker and one side for the lift.  Split the pump, not the flow.

Ted

kiran21 (Mechanical) · Answer 2 · 2010-04-17 16:44:01

It seems you have connected both the Motors in Parallel Connection through control Valve.

Parallel Connections are more efficient only when load on each motor is same. Raising the pressure on one motor cause the other one less efficient & may disrupt the speed relation. you can increase the system pressure to increase torque of highest pressure motor. How about connecting both the motors in series. speed of the motors can be controlled by bleed-off flow contol valve & torque can be adjusted by relief valves.

hydtools (Mechanical) · Answer 3 · 2010-04-17 20:32:48

Do not connect the motors in series. The motor shaft seals will not handle the pressure created by the downstream motor.
Do not manage motor torque with a relief valve. Permit the system to deliver what the motors require at the flows delivered to the motors.
Use relief valves only to protect system components.
Bleeding off flow from an upstream motor will deprive the downstream motor of flow that may be required to reach desired speed.

Ted

ozzy3406 (Mechanical) · Answer 4 · 2010-04-17 23:29:50

ted thankyou that makes sense the flowcontrols are after the spoolvalves. goes as such. from spoolvalve too in on flowcontrole then the controled flow goes to motor and from the motor back to spoolvalve the e flow on flowcontrole goes to tank. would it make any difference if i went straight to tank i wouldent think so since the return on the spool goes to tank anyways. is there anyway i can make this work or is there no way to?
kiran
these need to be independently controled the motors have two totally different loads and operate at different rpms so series is out of the question

hydtools (Mechanical) · Answer 5 · 2010-04-18 00:39:57

Change out your pump to a tandem pump, two pumps on a common drive shaft. Select each section to provide the maximum flow you want for each motor. You will have two separate motor circuits. Use separate directional valves. You can use the flow controls to control the speed of each motor.

Alternatively, you can use a rotary flow splitter between the single pump and separate directional valves. For about the same money as the rotary gear splitter you could just get a tandem pump to replace the single pump.

Ted

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