What overcentre valves do i need for my type r's ?

[zim]

Hi,

As per title really.... I've got a pair of milemarker type r's and i'm wondering if someone can advise me on which overcentre valves i need ? And where to get some ? All my piping and connections are 1/2" bsp.

What is the difference between single / dual ?

Thanks

Gordon

[chrism]

Good question, I also need to know this for my winches. Alfred Murray does sell them apparently and they are set up ready to go, but I would like to shop around a bit. Question for the hyrdraulic experts.. what is there proper name as I dont believe 'overcentre' is it? Correct me if im wrong but isnt it a check valve but crossline or something?

So for your question whats the diff between single and double. They are apparently used on tipping trailers so that when loaded and the trailer body is tipped and its COG goes past its hinge point it doesnt tip the last bit of at the speed of light, if you know what I mean!

[errol209]

I'm pretty sure of the following:

A dual overcentre is two single overcentre valves in one body. Since you are controlling a winch, which is reversible, you need the dual, one on each winch pressure line (as close to the winch as possible). This means the winch only moves when you tell it to, in either direction.

Pretty handy link here.

[jericho]

Since you are controlling a winch, which is reversible, you need the dual, one on each winch pressure line

Pretty handy link here.

I'm not so sure of the need for a dual valve.I can see the need to stop the winch line suddenly unwinding if a hose should burst.But i find it harder to imagine a case where a burst hose would cause the winch to wind in in a dagerous manner.

Personally I would not bother fitting a check valve of any sort to my hydraulic winch system if it were just to protect against burst hoses.I use synthetic winch line,and I have no doubt that the line will snap a hundred times for each time a hose bursts.

But I do have an overcentre valve fitted to my Milemarker for a slightly different reason.

Without it,if I winch the vehicle up a bank,and stop with the load still on the winch,there is pressure stored in the pipes from the spool valve to the winch motor.If I then go to lower the vehicle on the winch,it will drop uncontrolably until the pressure in the lines has equalised.Typically it will fall backwards two or three feet - an unpleasant experience.

My overcentre valve bolts directly to the winch motor - no pipes joining them.1/2" bsp ports comming out of the valve.They are available for any Danfoss motor,or copy of a danfoss motor (which is what type Rs are).I bought mine from Harrier Fluid Power,or what ever their name is.I could take photos if needed.

Best to decide what you need,then order it.Good advice on the confusing world of check valves is hard to find,even amoungst suppliers.

Excellent link there Errol!

[Bush65]

There are several points that are misunderstood and incorrect in this thread, which I will try to correct below.

Firstly I am not familiar with what motor is used on the type R - so can't advise on which overcentre valve to use. Most of these style (gerotor or geroller) motors have options for the inlet/outlet ports. Some of the options are designed for direct attachment of an overcentre valve - they have a flat machined face and tapped holes for the mounting bolts, o-rings (usually in the body of the overcentre valve) for sealing. Basic ports are threaded for hose fittings - in this case you would need to run a hose between the motor and overcentre valve.

Mounting the overcentre valve directly on the motor is preferred, but an in-line overcentre valve would be ok if the hose is adequately rated for the possible pressure, and is well protected against damage in use, rubbing against other parts, and does not have bends close to the end fittings.

what is there proper name as I dont believe 'overcentre' is it? Correct me if im wrong but isnt it a check valve but crossline or something?

Simple 'check valves' (also called non-return valves) allow flow in one direction and prevent flow in the opposite direction. A variation of this simple check valve is the 'pilot operated check valve' - when pressure is provided in the pilot passage it opens the poppet of the check valve to permit flow in the otherwise 'blocked' direction. A common industrial hydraulic application is has a load controlled by a 'double acting' (reversible) actuator (ram/cylinder or motor). Often we want the actuator to hold the load in the position where is is stopped by the operator. As it operates in both directions a pilot operated check valve is required and the pilot pressure is supplied from the line that is supplying pressure to drive the actuator (cross line). Then the check valve is shut (to hold the load) until we want it to move (when pilot pressure is supplied).

MileMarker hydraulic winches like the type R, do not have a mechanical brake and this function must be performed by a suitable hydraulic control valve. I do not recommend using the directional control valve for this because of internal leakage that occurs in the directional valve.

A 'pilot operated check valve' could be used, but it would be better to use a 'counter balance valve' (a special variation of a pressure relief valve), which is specifically designed for just this type of thing.

These would be ok if you only want to pull your vehicle up an incline and be able to hold it part way up the slope.

But they are not suitable if you wanted to lower you vehicle down the incline. In this situation, when the check valve is opened to allow the winch to reverse direction, the load will most likely cause your vehicle to run away out of control down the slope (you have no braking on the winch!).

This is why you need an 'overcentre valve' (this is the proper name). The overcentre valve is a variation of the pressure relief valve. They are adjusted so that the valve opens when the pressure increases to some value that is higher that the pressure that occurs due to the load that it is holding. They allow free flow in one direction (through an internal check valve) so you can winch up the incline, but when you stop winching the flow can't reverse when the line is trying to pull the drum around. If you want to lower down, you supply pressure in the other direction that causes the valve to open - when the vehicle tries to 'runaway' the pressure in the overcentre valve will drop below the setting and the valve will close.

Overcentre valves give very good control. They are the best and safest valves to use with our hydraulic winches.

Since you are controlling a winch, which is reversible, you need the dual ...

No. You only need a single overcentre valve.

Although the winch direction is reversible, the 'load direction' can only ever be in one direction - winch rope can only carry load in one direction. If you look at the brake on a Warn high mount winch, they have a ratchet so the brake only operates in one direction - likewise a hydraulic winch only needs to hold the load in one direction.

But dual overcentre valves are more common (there is more demand for dual's in industrial applications). There is no reason why you can't use a dual overcentre valve, and you won't have to think about which line to put the valve in.

[zim]

Thanks for the replies above.

I've got a single line overcentre valve, but got 2 winches hence me asking what type i needed.

So another single will do me fine for the other winch ?

The winches were previously run off a 12v solenoid setup, but i'm changing to a 2 lever spool bank.

Thanks

Gordon

[errol209]

Thanks Bush65, you've brought my knowledge on 200%!

While we're talking winch hydraulics, I am right in assuming for a hydraulicly powered worm-drive winch (like a 525 or Landrover mark II) the only protection I need is PRV acting to limit the motor torque?

[Bush65]

Thanks for the replies above.

I've got a single line overcentre valve, but got 2 winches hence me asking what type i needed.

So another single will do me fine for the other winch ?

The winches were previously run off a 12v solenoid setup, but i'm changing to a 2 lever spool bank.

Thanks

Gordon

As long as the flow rating of the single overcentre valve is equal or greater than your pump delivery it will be ok.

If you can get a spool bank with built in pressure relief valve, it can make for a easier and less cluttered installation.

[Bush65]

Thanks Bush65, you've brought my knowledge on 200%!

While we're talking winch hydraulics, I am right in assuming for a hydraulicly powered worm-drive winch (like a 525 or Landrover mark II) the only protection I need is PRV acting to limit the motor torque?

Generally worm gearboxes will hold a load (due to friction between the worm and wheel teeth) and not need an overcentre valve.

Yes you will need a pressure relief valve. The relief valve protects the system against over pressure (and limit motor torque as you said). For what we do (winching vehicles), I recommend a direct acting relief valve because their reaction times are quicker.

Compound relief valves are generally used in industrial hydraulics because the pressure rise from the crack pressure is much less. But when winching a vehicle up a rough track, the vehicle may slip and cause shock loading on the winch rope and winch system - a fast acting relief valve will cushion the shock much better (providing better protection).

[zim]

As long as the flow rating of the single overcentre valve is equal or greater than your pump delivery it will be ok.

If you can get a spool bank with built in pressure relief valve, it can make for a easier and less cluttered installation.

Yes, i've found a splice spool bank with relief valve.

Can you point me in the right direction on which overcentre valve to choose from this page : http://www.flowfitonline.com/acatalog/OVERCENTRE_VALVES.html

Thanks again

Gordon

Edit : Not too worry, Allan Byrne has them for £39 + vat. So i'll get one of them.