Simulate loading a variable displacement pump 4

[hydroman247]

Variable displacement on a large diesel engine.

How to simulate loading? Hand pump directly on LS and a PRV on the outlet of the pump going back to tank?

 

[hydtools]

Why not an adjustable valve on the outlet and return flow to tank. Connect LS line to just before adjustable load valve. Adjust the variable valve for different load simulations.

Ted

 

[hydroman247]

OK, that makes sense. I just thought that would run away but I just had a brain fail.

Thanks

 

[hydtools]

Or use something like a Webster flow and pressure tester.

http://www.webster-inst.com/applicationgroup/3

Ted

 

[hydromech]

I have just designed and commissioned a system that replicates the loading of a tandem pump set on train engine.

The pumps are Rexroth A10 and A11 piston pumps, with load sensing control.

I installed a Rexroth proportional pressure relief, with remote control via the vent line (X port). This works perfectly well.

Adrian

 

[hydroman247]

Yes, I am also dealing with an A10 Rexroth pump. I will be using a IH AR100 Relief valve I had lying around set to ~300bar.
When you say X port is a vent line, I have X marked as LS input.

 

[Oldhydroman]

On the Rexroth relief valve the vent port is labelled "X" on some other manufacturer’s valves the vent port is labelled “V” or “3”. I dare say there are other names as well. On the Rexroth A10 pump the load sensing line is labelled "X" but some other manufacturers call the load sensing port “LS”. On a CETOP/NFPA pilot operated DCV with external pilot supply, the pilot port will be labelled "X". Conclusion: the letter "X" can stand for different things on different components.

If you want to test your pump across a series of different pressure and flow scenarios then you could trick the pump to running as a pressure compensated unit (see below) and then vary the load on the pump by connecting a big throttle valve between the pump supply and tank. Make sure the throttle valve is the type that can be adjusted while under pressure. One with a knob or hex-key adjustement will probably be OK. A barrel style throttle valve probably won’t be OK. This is the circuit that Ted suggested - except I've used five times as many words.

You can make the pump run as a “pressure compensated” unit by connecting the load sensing port directly to the pump outlet and then setting the maximum pressure on the pump pressure compensator. Alternatively (this only works on Rexroth A10 units with a DFR type control) - wind in the load sensing pressure differential pressure adjuster to force that spool hard over - this converts the pump to a DR control and it doesn't matter what you do with the load sensing connection.

The problem with using a “relief valve” for the loading valve on a pressure compensated (or load sensing) pump is that the load setting will be a bit all-or-nothing: when the relief valve is set to more than the pump pressure compensator setting there will be no flow, when the relief valve is set to less than the pump pressure compensator setting there will be full flow. You might be able to set the relief valve just high enough to balance the particular characteristics of the valve and the pump but it won’t be easy and the load setting will drift as the temperature varies.

For a full test of the operating envelope of the pump you need a needle valve on the outlet of the pump with a “load” relief valve downstream of that. (The pump still needs to be protected by its own safety relief valve.) The load sensing connection should now sense the pressure on the outlet of the needle valve. You can then set the load pressure on the “load” relief valve and adjust the opening of the needle valve to control how much flow the pump pushes across the “load” relief valve. You will be able to investigate everything between: tiny flow with low pressure, maximum flow with low pressure, tiny flow with high pressure and (if you have enough power available) maximum flow with high pressure. Your "high" pressure setting on the “load” relief valve needs to be a little bit less than the pump maximum pressure compensator setting otherwise the pump won't deliver and the test will yield no results.

DOL

 

[hydromech]

When I say X port, I mean the X port on the valve. I am not controlling the pump flow, I am just putting a load on the pumps.

 

[hydroman247]

Well, the test is actually for the diesel engine and we just want to use the pump that is currently on there to load the engine for a while, could be an hour or more.

Because of this, I am inclined to go the simple route of plumbing LS to the pump outlet and putting a relief valve then back to tank on the main supply. Set the relief valve on its lowest setting, start the engine and just increase the spring pressure until pressure rises over LS and swashes the pump and I will have full flow and the pressure will be increasing as the releif valve setting increases.

I wouldn't need to touch LS or Power control settings on the pump itself then and I wouldn't risk any damage. Of course keeping an eye on oil temperature at all time.

The picture attached is the idea that should work.

Thanks for all your help.

 

[hydroman247]

It needs to be under full load which is why the relief valve will be set at 330bar which is the maximum system pressure on this machine.

 

[hydromech]

The load on these pumps is from a hydrostatic fan drive and an alternator that powers the train. Since there is no alternator because the engine will be in a test cell, I have used a proportional pressure relief to simulate the 49kW load from alternator. The vent line (X) has a locked relief valve on it to limit the max pressure and there is also a NO 2 port directional control valve to drain the pilot stage and effectively switch the valve off to prevent pressure building.

There is a DRL pressure controller on the pump with LS control. These are switched of, so the A11 pump cannot adjust its displacement. The pump max displacement is 98 LPM, so I have allowed them to go up to 300 BAR as I don't know what efficiency they will achieve.

The strategy is to start with 0 Volts on the command signal, with the X port open to dump the pilot pressure. When the engine is up to the rated speed, the valve on the X port is closed and the command signal is ramped via a remote controller.

The hot oil leaving the valve goes through a water/oil heat exchanger before returning to the reservoir.

I have put a pressure filter on the outlet of the pump to protect the proportional valve.

This is on a 550kW engine and as I say...it works very well and is perfectly safe.

 

[hydroman247]

Might as well pop this question in here rather than start a whole new thread.

When fitting a spool type flow divider/combiner into a drive circuit, which is more ideal for the most used direction. e.g. Forwards would be the most used direction so should it go DCV>Divider>Motors>DCV Return or DCV>Motors>Combiner>DCV return? I know it doesn't make much difference in real world terms, but I had it in my head that one way was more efficient than the other.

I have googled and come up with no answer.

Thanks.

 

[automatic2]

for hydraulic top drives we'd stack 6 pumps behind a 1200hp diesel. Watch your ability to dissipate the heat.

 

[hydroman247]

Oil temperature is monitored of course. I did a quick test yesterday and it worked fine with LS just looped back to pump and relief valve set open and just wound in until the required pressure.

Thanks guys.