743B With low pressure?

[sirbean]

OK I need to make sure I'm not missing some thing here. I just replaced my hydrostat/pump assemble plus drive motors. You guys helped me identify the steering problem and it was the pump. Good news is steering is fixed. Bad news is now I can't get more than 600psi out of the pump the runs my cylinders. I installed a needle valve on the output of the pump with a guage in between them. As I squeeze the flow off pressure rises then levels off at 600 at idle. 900 to 1000 psi with engine wide open. OK I got a bad pump. So I take it off and send it bad. They send it back and tell me it is fixed except it does the same thing as last one pump. Am I missing some thing?? Could use you guys help here before I call pump guys and chew some arse. I didnt have any pressure problems before I installed this pump . By testing the way I did I have eliminated everything down stream from pump and dont think I have a upstream problem as it runs pretty quite. No sounds of cavitation. Thanks.

 

[Mikefromcny]

Are there any pressure relief valves that could be partially stuck open in your system?

 

[sirbean]

Are there any pressure relief valves that could be partially stuck open in your system?

There are reliefs in the control valve but it is down stream from where I am squeazing the flow on the pump which should eliminate any thing down stream from needle valve. I also made sure there was no pump drive slippage by putting the machine against a tree and the wheels will spin or stall motor depending on engine rpms. Thanks and help 8-(

 

[sirbean]

There are reliefs in the control valve but it is down stream from where I am squeazing the flow on the pump which should eliminate any thing down stream from needle valve. I also made sure there was no pump drive slippage by putting the machine against a tree and the wheels will spin or stall motor depending on engine rpms. Thanks and help 8-(

Put a flow meter on it today and at 2500rpm it had 7.75 gpm with 200psi load. Supposed to be 12.1 gpm. Start to restrict flow and at 1000psi it was doing 1.5 gpm. No doubt it is the pump. Pump builder didnt argue and is sending me a new pump. Do you guys think anything on supply side could cause any problems. This has me gun shy and am starting to question myself. When I pull the outlet side hose off pump oil shots out a couple of inches . That is just gravity feed oil from tank. Oil goes from tank through cold oil bypass valve to inlet side of pump. Anything to check or am I just being worried over nothin. What do they act like when you have a small leak on suction side? Is a small amount of foam normal in tank? Thanks again!

 

[Tazza]

Put a flow meter on it today and at 2500rpm it had 7.75 gpm with 200psi load. Supposed to be 12.1 gpm. Start to restrict flow and at 1000psi it was doing 1.5 gpm. No doubt it is the pump. Pump builder didnt argue and is sending me a new pump. Do you guys think anything on supply side could cause any problems. This has me gun shy and am starting to question myself. When I pull the outlet side hose off pump oil shots out a couple of inches . That is just gravity feed oil from tank. Oil goes from tank through cold oil bypass valve to inlet side of pump. Anything to check or am I just being worried over nothin. What do they act like when you have a small leak on suction side? Is a small amount of foam normal in tank? Thanks again!

Good to hear you have some fancy test gear to check flow and pressure. There is no reason why you should be getting such a low flow and pressure. This is a vane or gear pump? silly question, but the rotational directions are matched right? vane pumps you have to ensure the centre plate is the correct way around, a gear pump needs to be bolted together right at the shop.