i have a hydraulic motor with attac

[alba2]

i have a hydraulic motor with attached brake unit. this brake unit needs a min of 12bar pressure to release
the brake, upto a max pressure capacity of 30bar.
if i pipe in a feed thru a solenoid valve and then thru a pressure releif valve set at 20bar i think this would release the brakes. my issue is 1-will this not boil the oil when brakes are off for a long time?as pumping flow thru pressure releif constantly. 2-when the valve dumps then repressurises the system will this not cause a fast on off of the brakes in a repeating cycle? 3- is there anothere valve i need that controls the pressure specific to this kind of application?
thank you

 

[LittleInch]

What's your main system hydraulic pressure?

Can't you get your 20 d/s a pressure regulator, not a pressure relief?

How would you restrict flow in this system?

Can you draw it so we're not confused?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hydtools]

It sounds like you are shutting off flow to the brake with a solenoid valve. Therefore, no flow through the relief valve when the brake is off, released. No heat generated. Heat will only be generated when the brake is activated. No? Does the system have the heat rejection capacity, a heat exchanger, to reject the heat generated? Open or closed center system?

Ted

 

[alba2]

hi all, thanks for your help, i wasnt aware of a pressure reducing valve, i think this is what i need as it will hold pressure at 20bar and also let excess oil flow to tank? the brakes are sprung so i need constant pressure to release them, with no pressure and oil flowing to tank the brakes are on. motor is poclain ms18 shaft with t12 brake unit.

 

[LittleInch]

Better called a Pressure Regulating Valve - always spell out what PRV means as there are many things which are the same abbreviation but different....-

This will generally lock up, i.e. no flow if the pressure goes above 20 bar.
You still need a Pressure relief valve downstream in case the regulating valve doesn't seal 100% with return to the tank set at say 23 or 25 bar, but it will only flow a small amount, if at all.

To activate the brake your solenoid will need to be two way acting and dump the pressure back to the tank whilst sealing off the 20 bar supply.

What is your main hydraulic supply pressure?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[alba2]

brake is a standalone circuit, so i assume that when brake on and dumping to tank then press almost zero other than friction in pipes, but 20 bar when flowing thru PRV plus whats is oil diverted back to tank friction pressure? wont know i suppose til i build it and see what the psi reads on the pump outlet. the motor supply is separate closed loop circuit.

 

[LittleInch]

When brake is on there would be no flow to the brake cylinder circuit.

Your incoming solenoid valve needs to be double acting three port valve which connects the line to the brake cylinder to either the incoming 20 bar supply or the tank drain. Only one of those is connected to the brake circuit at anyone time.

This is all very basic stuff so I'm getting a bit worried that you're not experienced enough to be doing this work without someone else near you checking and approving it. Get it wrong and to your brake might not work or your hydraulic system will fail.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Jacc]

LittleInch, I've never seen the term Pressure Regulating Valve being used for anything other than pneumatic pressure regulators. While the hydraulic version technically does the same thing I don't think you'll find many hydraulic suppliers calling it that. The name most commonly used is pressure reducing valve. Google responds well to this.

 

[akkamaan]

I would help a lot in a opening post by telling us what type of application this is about.

i have a hydraulic motor with attached brake unit. this brake unit needs a min of 12bar pressure to release

So the brakes are applied mechanically with a spring?

upto a max pressure capacity of 30bar.

As I understand you the brake release pressure is supposed to not exceed 30 bar, right?
And the rest of the hydraulic system has a higher max pressure of 150-200 bar or whatever?

the brakes are sprung so i need constant pressure to release them

I read between the lines that you need the brake to be released even when the pump pressure is lower than 12 bar, right?
I also assume you have a regular constant flow system with a fixed displacement pump. That means you have to build a separate constant pressure system for the brake circuit. Then you will need an accumulator AND a check valve. The accumulator can then uphold the minimum pressure for the brake release system even when pump pressure goes low.
A pressure-reducing valve focuses on pressure and not flow. You will only need pressure to KEEP the brakes released. A small flow is only needed during that short moment the brake cylinder strokes to release the brakes.

A constant pressure system with an accumulator is always subject to internal leakage and after some time the accumulator needs a re-charge. That can built with automatic recharge. Otherwise, you have to rely on recharging when the motor or other actuators are activated in the system
The accumulator needs to have enough size to maintain the "20 bar" constant pressure as long as needed.

Mobile Hydraulics

 

[BEMPE16524]

not sure what is your application, but here is what I use in my system so far. Just to share some idea.
it is a winch system with by-directional rotation. the shuttle valve allow pressure input to the brake release line if pressure coming from both intended rotation.

you can add check valve at the drain line.

R.Efendy