By Josh Cosford
There are a couple of methods used in the mobile hydraulic market to control multiple actuators from a common pump supply. The most simple is the monoblock valve, which typically has a cast iron housing and a machined spool operated by a spring centered lever, although solenoid operation is available for nearly every brand of valves.
The monoblock valve is available up to at least eight spools, each able to operate a function of their own. The most basic of these valves have no auxiliary valves except a relief common to the pressure ports of every spool. Although rare, monoblock valves can be optioned with components in the inlet or work ports of the valve, such as pressure compensators or work-port relief or counterbalance valves. If you are a mobile OEM using hundreds or thousands of the same configurations, a monoblock valve is the simplest direction to take.
If you have a more demanding circuit—or if you manufacture machines each with unique build requirements—sectional valves could be the product for you. Sectional valves, unlike stack valves, are slices of individually packed spools held together horizontally with tie rods, and include both inlet and outlet sections. If you require just one spool section, you still need one inlet section and one outlet section, on top of the tie rod kit.
Sectional valves can be highly optioned with relief valves, pressure compensators, load sensing functions, work port auxiliary valves etc. A large OEM can stock dozens of individual components, and not unlike modular stack valves, create complex circuits on the spot. There are almost no mobile machines without some valving located outside the centralized bank closer to the actuators, but this method gives you a lot of options to minimize that.
Most mobile directional valves come with a configuration—usually via a plug or sleeve—called “power beyond.” Power beyond can be a difficult concept for those not familiar with fluid power, or for some whom come from an industrial hydraulic background. Unlike “tandem center” valves, which in neutral position flow from pressure to tank, allowing you to use fixed pumps without unloading valves, or to use the tank flow for downstream functions, power beyond allows you to hook up another downstream valve, while leaving the first valve to operate normally.
A power beyond valve has three internal flow cores: The pressure core, the tank core and the through-center (or power beyond) core. If unused, the tank and through cores are open to a common port, and flow goes back to tank as it would in a tandem centered valve. However, when the power beyond adaptor is installed, the through center core is separate from the tank core. The tank port of the first valve still needs to go directly back to tank, but the power beyond can now feed into the pressure port of the next, downstream valve.
The advantage to power beyond is in allowing you to hook up optional sub-circuits to a standard configuration, like adding a log-lift function to a log splitter. The downsides are the extra plumbing, which lead to leaks, and also an annoying effect related to the first valve in the chain tending to steal flow for its operations. Because the first valve has its own tank line, every function used by that valve diverts flow away from power beyond and straight back to tank. So if you’re running a motor function on the power beyond side and decide to operate a cylinder via the first valve, you will temporarily stall the motor until the lever is released upstream.
Josh Cosford, Certified Fluid Power Hydraulic Specialist, is with www.fluidpowerhouse.com.
Hi Paul,
I’ve got a question for you. On my Woods backhoe, the Bucher stack valve has the pressure inlet line on one side and the return to tank line (outlet) on the other side. In that outlet section it has a Power Beyond plug that can be utilized if one wants. So what I see is, with all valves in neutral, the flow is circulating. Near there I’ve mounted an auxiliary (open-center) valve that will be used to operate a thumb on the bucket. The question is, could I just run the return line right into the inlet of the auxiliary valve and the outlet from there back to the tank?
Thanks, Don
Hi Don,
To answer your question accurately, I’d have to know the part numbers of the valves in question. I’d hate to give you poor advice based on assumptions. Often those in the mobile hydraulic industry interchange the terms “open center” and “through-center.” Just because a valve flows from pressure to tank in neutral, it doesn’t mean it’s open center, which refers to all four ports being connected in neutral. Through center just means the valve bypasses the spool in neutral, but the spool could be open center, motor spool, closed center etc.
Regardless, if your auxiliary valve is a mobile-type through-center valve, it will work just fine after your Bucher valve. Just remember that the first valve gets flow priority. Thanks,
Josh
I have been looking all over for an answer to what I consider a simple question. I have a directional “orbit” valve that has a power beyond port and have no need for it. It stalls the pump when plugged. So my questions is. Where do I relieve the pressure from this and how?
Hi Jeff:
I’m not sure what a directional “orbit” valve is. Regardless, just be sure you still plumb the tank line of the first valve back to tank. This means your first valve will have two hoses attached to the one side; one for the tank line, and other other will go to the pressure port of the downstream valve. Also, ensure your tank port is connected on the last downstream valve.
I think you’re seeing a situation with no tank flow, and when you try to activate a function, it stalls out your system because your flow has nowhere to go. I hope this helps!
Josh Cosford
Hi Paul, I have built a log splitter with a hydraulic log lifting boom. It has a 20 hp V Twin engine, 28 GPM pump, 30 GPM detent, open center valve with power beyond, 3/4 inch pressure hoses 1 1/4 inch return lines, 50 GPM filter, 35 gallon oil tank, the return line off the main valve is 3/4 inch feeding into the 1 1/4 inch line and the return line of the boom valve is 1/2 inch feeding into the same 1 1/4 inch via a tee. I set the relief pressure at 3000 PSI, The first time I ran it for around 1 hour and the tank was almost too hot to touch, can you see anything wrong with my choice of parts and why it got so hot. the pressure at idle is almost 1000PSI, Thank you for your time and any suggestions, Geoff. splitter and boom works great.
Want to supply a wood splitter from a tractor PTO supply. Tandem lever valve controlling the top link and lower arm leveling cylinder has the tank return line as supply to the front end loader controls and the power beyond port supplying a bucket clamshell controller. Can I use the tank return line from the front end loader control valves as supply to the wood splitter valve or do I need to go from an unused power beyond port on the loader control valve? When I’m using the splitter will not need to operate the other tractor hydraulics.
I need to replace the out rigger 2 spool valve on a 1962 Wagner Backhoe. I can not find any information on this equipment. As you probably know the back hoe has 4 levers on two different control valves. Are these hooked in series or is this a power beyond set up?
I added a third function solenoid controlled valve to john deere 5205 so could add buttons to joystick for open close on brush grapple. Plumbed it from the power beyond portlike the directions said. Cylinders will not respond unless engine is revved to around 1500 rpm. Loader lift and curl function still works at idle speed. Why will grapple open close not work at idle speed.