Hydraulic problem

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cbrew
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Re: Hydraulic problem

Post by cbrew » Mon Dec 18, 2017 11:07 am

Dale_F wrote:Chris - you are correct. There is no provision for a min rpm -- or idle speed in this setup. To go, you run the electric motor when turns the pump. When you stop, the pump stops. No idle speed.

I see a trend towards replacing the vane pump with a geared pump (if 2 votes is a trend!). I will keep "voting" open in case someone has a cheaper, less messy option!

Seriously - thanks to everyone who has read this, and to those who have offered help.
have you looked into just stepping up and removing the hydraulic system all together? using the same motor, you can go with a center drive setup. selling off the hydraulic components will help off set the cost. you know there has to be waste in the form of heat and friction in the hydraulic system so comparing the two systems. it will likely we a wash when it comes to efficiency. just a thought
If it is not live steam. its not worth it.

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warmstrong1955
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Re: Hydraulic problem

Post by warmstrong1955 » Mon Dec 18, 2017 11:09 am

If I understand how your system is working, you are able to slow down or stop the pump, without shifting the solenoid valve out of forward or reverse?
If that's the case, when you stop the motor, and stop or slow down the supply of oil from the pump, you create an over-running load. The inertia of the loco still wants the flow of oil to the traction motors, which is no longer there, hence, it pulls a vacuum.
If you have an open center solenoid vale, with open center transition, you would have to shift it into neutral, before slowing or stopping the pump.
Or, you could add some anti-cavitation valves, which are typical on hydraulic systems that can see an over-running load. That includes hydraulic drives, and cylinder systems. Typically anti-cavs are built into the control valve, and most often inside the spool, and I doubt your solenoid valve has them. They can be added externally. Very often, a counter-balance vale is used, which includes relief valves and anti-cavs in a nice neat block.

Cavitation should not be confused with getting air in the system. Cavitation, is not air, it is vacuum bubbles....not air. When they get to a point in the system where the oil is re-pressurized, even to 0 pressure, the bubbles implode. They can suck pieces seals, of cast iron and steel and brass, right out of valves and pumps. It's ugly.
Air, is not such a big deal. It makes systems sluggish, spongy, and noisy, but does not do the damage that cavitation does. Vane pumps don't care for air so much, they don't like the lack of lube. Gear pumps will handle a lot of air, require less lube, and make good scavange pumps because of that.

Bill
Today's solutions are tomorrow's problems.

rkcarguy
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Re: Hydraulic problem

Post by rkcarguy » Mon Dec 18, 2017 11:42 am

It seems odd to me that this system has an electric motor attached to the type of hydraulic system typically used behind a gas motor. Being it's electric, and you return the throttle(and electric motor) to zero rpm, the inertia is going to keep things going forward and pull air into the system. A gas engine would obviously idle and maintain some hydraulic pressure, and therefore combat any "vacuum bubbles" from forming. The easiest way to fix things would obviously be to set up your electric motor with an "idle" so the hydraulic system always has pressure. At least try it, it will help determine what the problem is if nothing else.

Dale_F
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Re: Hydraulic problem

Post by Dale_F » Mon Dec 18, 2017 11:44 am

Chris - Yes - we have spent a lot of time talking about just pulling the hydraulics and converting to all electric. That is an option, but if we are "close" and can do something fairly easy, then I would like to, for now, stick with this option.

Bill - I would suspect you are correct - there is no anti-cav option on this spool valve. Can I add one externally? Where would I add them, and can you tell me where to go look for them to purchase? Thanks!

John Hasler
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Re: Hydraulic problem

Post by John Hasler » Mon Dec 18, 2017 11:58 am

All the suggested changes are good but adding a check valve in parallel with the pump and making sure the pump inlet is well below the minimum tank fluid level should suffice to get you going. You should have a relief valve, though. Is one built into the pump?

One possible reason for using hydraulic motors rather than direct electric drive is lack of space. The overall design is "puzzling", though.

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warmstrong1955
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Re: Hydraulic problem

Post by warmstrong1955 » Mon Dec 18, 2017 12:03 pm

Something like this Dale: http://www.sunhydraulics.com/model/YRDK
Sun makes them is various flows. It would mount between the control valve, A & B ports, and the motors. Advantage to Sun, besides being a good product, is they have a lot of dealers.
Last I was buying Sun products, among many other hydraulic components, I was using Hydraulic Controls Inc in Stockton. I've also gone through them in Denver, and SLC. All good people that I dealt with.
If that's not close, look here: http://www.hydraulic-controls.com/index.php/locations
They have a lot of brands, and are quite helpful. Good idea, if you can, would be to get an ISO schematic from whoever built your system, and talk to a guy at HCI, or at another Hydraulic House, and start off with sending a copy to them. Most of those places are still old school, and have technical people that actually know about their products.

Bill
Today's solutions are tomorrow's problems.

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warmstrong1955
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Re: Hydraulic problem

Post by warmstrong1955 » Mon Dec 18, 2017 12:51 pm

Dale,

While I am waiting for some welds to cool, so I can machine.....

I scrounged this up on the interweb.
A bit of info for you that may help.

http://www.hydraulicspneumatics.com/200 ... ifoldsHICs

Bill
Today's solutions are tomorrow's problems.

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