Hydraulic dyno

na2slow2

Member
Just got the dyno finished trying to make runs with it. When everything is cold it will load up with my valve, but after a few seconds I can turn it by hand with my valve shut. It's a needle style valve. I'm thinking the valve has a built in bypass or something. But it's not loading up at all. But after I turn it off I can wait a few minutes and it will load up again. When it loads up I get pressure on my guage. Anyone else have this problem. Thanks
 

95 shaw

Premium User
Positive displacement pump, with positive shut off needle valve, and no relief valve, will equal broken pump.

Somewhere in the system, air is entering, or pressure is being bypassed.

Gear or vane style pump?
 

na2slow2

Member
I believe it is a gear, project has been going on for a year. So I will have to research where I even got the pump. When we take the hose off and spin slow it pumps like crazy, tack it up it stops.
 

95 shaw

Premium User
Check rotation first.

If gear pump, or vane, will move a little oil to least resistance.

Check for debris in relief valve, if has one.
 

alvin l nunley

New member
what are you using to analyze your data acquisition? I have a program you might like if you have a computer and Excel software. It's free. It also produces a chart showing your horsepower and torque curve. The curves are corrected to the prevailing air pressure and temperature. You can enter the pressure that the pump is producing and there is a factor number that you can adjust so that the torque number is very close to correct.
 

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Chris Cooper

Premium User
Best pump on the market - Rexroth. But I am a little biased.

For what you're doing, you don't really need a high end pump, unless you can find a great deal on one. The biggest thing is to find a positive displacement pump and a good solid relief valve (the faster acting the better). If you can find an inexpensive proportional relief and have a way to control the valve, you can do quite a bit as you get better with the controls.

If you find a vane pump, make sure you spin the pump at rated speed (or as close to it as possible). The vanes need a certain RPM to insure they seal against the stator. Rexroth has a pump that operates at lower speeds as does Denison (now Parker); not sure about Vickers.

The least expensive and most dirt tolerant type is the gear pump. Wide varieties are available. There are several hydraulic surplus supply companies on the web that offer pumps from various manufacturers. I've built a few dynos with the Rexroth PGH pumps and have had great success.

Hope that helps.
 

flattop1

Dawg 89
what are you using to analyze your data acquisition? I have a program you might like if you have a computer and Excel software. It's free. It also produces a chart showing your horsepower and torque curve. The curves are corrected to the prevailing air pressure and temperature. You can enter the pressure that the pump is producing and there is a factor number that you can adjust so that the torque number is very close to correct.
Did you improve your spread sheet or is this something new ?
If it would work with a water brake I would be interested .
 

na2slow2

Member
3.11 cu in Dynamic GP-F25-51-S13-C Hydraulic Pump
That's the one I got, also a relief valve too. Thanks and eventually I will need the spreadsheet stuff..
 
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