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Curtis B.
Curtis B., Technician
Category: Construction and Road Equipment
Satisfied Customers: 1167
Experience:  Technican turned service manager with multiple lines of equipment and rental units.
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The other day we took the Valve apart the one up front which controls the front bucket

Customer Question

Hi the other day we took the Valve apart the one up front which controls the front bucket on my backhoe. The reason we did was it didnt have any down presure for a few months but the other day as I was loading a dump truck it didn't lift very well either so I just figured the o-rings in the vavle were old, so we took it apart, and yes the O-rings were old and not working correctly. Well we put it back together and Now non of the Hydraulics work not even the boom and steering "which worked fine earlier". We put a gauge on the Hydraulic pump and the pump is not putting out any pressure, do you have any Idea what the problem could be.
Submitted: 2 years ago.
Category: Construction and Road Equipment
Expert:  catmastertech replied 2 years ago.
Try holding a backhoe valve in "stall condition" (pull bucket lever and hold it in) then try operating steering and loader functions while holding the lever applied. If this brings the pressure back, you have a resolver check ball stuck open or missing.If this does not help, steering priority valve must be stuck or assembled wrong. Let me know what you find and the full serial number of this machine with your reply.
Expert:  catmastertech replied 2 years ago.
The inlet section also has a resolver. If this is missing, this could be your problem but, it depends on the model and serial number.
Customer: replied 2 years ago.
this is a Cat 426b serial number : 5YJO1975, We just took the main Hydraulic pump off today thinking that might be the problem, we also took it apart and it looks just fine. The resolvers were fine thats why we didn't replace them we just replaced o-rings.
Expert:  catmastertech replied 2 years ago.
Did you check for missing check ball in each of the secondary resolvers?Is the unit down now were you cannot perform the test I suggested earlier?
Customer: replied 2 years ago.
We had tryed what you said earlier as far as holding one lever in and moving others around and it didn't do anything. And my mechanic says the check balls are there, there's only 2 Resolvers in this valve says my mechanic , but I'm not not sure what you mean by secondary resolvers.
Expert:  catmastertech replied 2 years ago.
He may have missed the resolver in the inlet section for the steering priority valve.A two valve loader valve will have three secondary resolvers. These are the ones in the back side of the valve. They control the load signal between each valve section.Primary resolvers are in a captured check valve assembly in the bottom of the valve. They control the load signal between each side of the cylinder. (The steering does not have a primary resolver.)
Expert:  catmastertech replied 2 years ago.
Here are details about the resolver network. Signal Resolver Network TroubleshootingThe signal network can be easily checked. Start the engine and warm up the hydraulic oil. Run the engine at LOW IDLE for this check. Connect a 30 000 kPa (4000 psi) gauge to the signal line pressure tap. Operate each control lever in the following order:1. Left stabilizer.2. Right stabilizer.3. Boom.4. Swing.5. Backhoe bucket.6. Stick.7. Extendible stick (if equipped).8. Loader lift.9. Loader bucket tilt.10. Multi-purpose bucket (if equipped).11. Steering.Work each implement against a load. Watch the gauge. Maximum system pressure should be seen for all circuits. By using the gauge, small leakage problems such as cut or missing seals can be detected. Secondary Resolvers (Two or More Valve Sections)If two or more control valves in series next to each other fail to work normally, the problem may be in the secondary resolver of the first implement control valve that is closer to pump supply that does work properly. This control valve's secondary resolver is allowing signal pressure from any control valve further from pump supply to leak through to either the rod or head end signal passage of that control valve to tank. This leakage may be caused by a ball not seating against the drain side of its resolver causing the valve to not function properly.This holds true unless; the ball is missing; there is debris preventing the ball from seating properly; the seal is missing or leaking when multiple valves malfunction. Operate the malfunctioning valve farthest from the pump and at the same time start going through the previously mentioned valve order. The first valve that makes both of the implements work, is the one with the bad secondary resolver. What is happening is that the farthest valve is sending a signal and the valve with a bad seal or missing ball is also sending a signal. When both signals meet at the valve with the bad secondary resolver the leak has no impact on the signal that now goes to the pump and it has no effect on the flow control valve. Primary Versus Secondary ResolverFor valves with a flow control spool, if only one valve section either fails to work in one or both directions or works slowly in one or both directions, the primary or secondary resolver in that control valve may be bad. To determine which secondary resolver is bad perform the following check. Stall an implement further away from the pump than the valve in question. This will force the ball in the secondary resolver to seat away from the drain side of the resolver. This eliminates the possibility of a leak on the drain side of the secondary resolver. Now operate the suspect valve while holding the other implement in stall. If it is still operating slow in one or both directions, then the primary resolver may be bad.If the primary resolver is bad, then the pressure bleed off caused by the bad resolver is affecting the operation of the flow control spool (if so equipped) in the valve body. The effective force (signal pressure + spring) trying to open up the valve to allow flow to the cylinder is insufficient to meet the cylinder load requirement so the implement has a slower response.Normally if an implement is slow in both directions, the problem is usually in the secondary resolver. If an implement is slow in one direction it is typically caused by a bad primary resolver (caused by debris or bad seals).Other causes of malfunctioning valve sections might be a misadjusted linkage, a broken pressure reducing valve spring, the flow control spool incorrectly installed or bad line relief and/or makeup valves.NOTE: If there is debris in the system. It is recommended that the system be flushed by removing all the balls in the secondary resolvers and operate the implements. Enough flow will be supplied to flush the debris to the tank.
Expert:  catmastertech replied 2 years ago.
This image shows the circuit.

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