Hydraulics Question

Hello all,

Im in the process of building a hydraulic post hole auger. Hydraulic motor driving the auger by chain and sprockets ect. Where i run into some questions is how to rig up the hydraulic controls. The tractor i plan to run it off of is a ford 4400 with a front hydraulic pump and loader. I would like to keep the loader functional while using the auger without having to switch hoses back and forth constantly. I have ordered a 30 gpm single spool open center hydraulic valve for a log slitter to run the hydraulic motor. This should give me forward and reverse on the motor. The motor is a low speed (200 RPMS) high torque so im not to concerned about a hammering effect when the motor is shut off. What i need to know is if i install the new valve in series downstream of the existing 2 spool valve for the loader are there any problems i need to be aware of. I will adjust the pressure relief to match the tractors spec max pressure. I've had to replace the spline coupler between the pump and motor once before and ide like to avoid doing that again. Running the valve in series downstream should mean simply plumbing the existing 2 spool valves output into the input of the new valve...ect. This would give me 3 controls that could be operated independently one at a time. I could also easily keep adding valves this way later down the line if i wanted.

If anyone could give me a reality check of whether this will work or not it would be much appreciated.

I guess my main concern is having 2500 PSI in the out port of the existing valve that is probably meant for only a few hundred PSI.

Nope nope, gotta have a power beyond valve and add it BEFORE the current loader valve.

You have the right concern with the pressure in the outlet port. It will probably work fine. Where you could run into issues is if you plumb another valve downstream from your motor valve. If you have a motor in operation, then build pressure on the outlet of that valve, it can blow the shaft seal in the motor.

The proper way to run valves in series is to use power beyond valves closest to the pump. A power beyond valve has two outlets. One is the excess pressure flow piped in series to the next valve. The other is the return from the actuators, which is sent back to tank.

It would be very easy to keep the motor valve at the end of the system. I only envision using it to control the hydraulic motor a few times a year anyway. I will probably use it to control one of the links on my rear blade most other times with some quick connects. From the research ive done ive seen both recommendations to use a power beyond valve and people saying you can run as many open centered valves in series as you want. It sounds like the main concern without using a power beyond valve is that you can get pressure built up in between valves that shouldn't be there. I'm having a hard time understanding that though. If all the valves upstream and downstream are open centered there should only be pressure upstream from the valve. Valves upstream would be in there centered position allowing only flow to the next valve. When you move over to using another valve it will be the same way with all pressure downstream being released to return to the reservoir.

My understanding is that power beyond is only needed if you want to control another valve downstream at the same time.

Where you can get into trouble is if you run two valves simultaneously when the first one is not a power beyond one. Then the pump will end up with the pressure of the first use plus the pressure of the second valve. I've been told that can cause pumps to blow apart.

Wouldn't the pressure just max out at the relief pressure of the furthest downstream valve?

I think you'd be better off mounting your directional valves on a manifold. Be careful not to deadhead your pump, especially if it is a positive displacement pump. I'd also install some gauges so you can tell if you have some trapped pressure when the system is shut down.

The relief on your main valve dumps
pressure to the out port to return to the
tank. Now you block that path and bad
things happen to good pumps etc

So it sounds like i can do this as i planned...however if i were to grab two levers at one time i could potentially damage some things. I believe I understand the delema as pressure relief valves work with assuming that there is near zero pressure on the DS side. If there is pressure in the DS side it could potentially trick the pressure relief into releasing at a higher pressure than as set. So if i had a loader valve engaged and the loader hit max pressure and i had back pressure from the motor my pressure relief in the loader valve could malfunction and result in a higher pressure than the max.

I guess this could all be solved by a independent pressure relief valve plumbed in upstream of all of the valves? Set to drain into the reservoir return line. Still not the proper way but it would protect the pump and or having to replace the spline coupler...again.

All I can say is if that works I sure have spent a lot of money on power beyond valves over the last 30 years. And yes I have seen the seals blown out of valves and pumps from bad incorrect plumbing.
Hope it works for you