Rotate Circuit on Deere/Hitachi EX150-160

[MikePhua]

Background
The Deere/Hitachi EX150-5 (and similar models like the EX160) is a mid-sized excavator widely used for general earthmoving, utility, and demolition work. As part of its hydraulic system, it uses a pilot pump housed inside the main pump’s bell housing. The pilot pump supplies control (pilot) pressure for the machine’s multifunction control valve that operates boom, stick, bucket, swing, etc.
A grapple rotate circuit is an additional hydraulic function (an “option spool” or auxiliary function) that allows rotation of an attachment like a grapple. Users sometimes want to add this control so that they can rotate grapples in addition to the standard functions.

Problem Statement
When plumbing (installing) a grapple rotate circuit on the EXP machine, the following issues were observed:

• The pilot pump being inside the bell housing prevents using a tandem pilot pump (i.e. one that could supply extra pilot flow independent of or in addition to the existing pilot pump).
  
• The rotate circuit, when connected to a test port, works, but if another function (like boom or stick) is operated at the same time, the grapple rotation spins too fast (overruns), or behaves erratically.
  
• The solenoid valve installed for the rotate function has an internal relief, so at least in principle it should protect against overpressure relative to system pressure.
  

Technical Insights & Terminology

• Pilot Pump: Provides low-pressure hydraulic flow used to operate control valves rather than doing the heavy lifting (which high-pressure work pumps do).
  
• Bell Housing: The enclosure around the main hydraulic pump; in this case, the pilot pump is located there, making it less accessible or modifiable.
  
• Option Spool / Auxiliary Spool: A dedicated control spool in the main control valve or hydraulic manifold that allows additional hydraulic functions beyond the standard boom/stick/bucket.
  
• Relief Valve: A safety device built into hydraulic circuits (or solenoid valves) that opens when pressure exceeds a set threshold to protect hoses, valves, etc., from overpressure.
  

Contributing Factors to the Issue
Some factors that contribute to the rotate circuit behaving poorly under load include:

• Shared Pilot Pressure Demand: When multiple pilot-demanding functions are used simultaneously (rotate + boom + stick), the pilot pressure may drop or fluctuate, affecting responsiveness.
  
• Flow Capacity & Hose Routing: The branch to the rotate circuit from test ports or tees might not have the correct sizing or routing, causing pressure loss or delays.
  
• Lack of an Independent Pilot Source: Without a separate/tandem pilot pump or dedicated pilot supply for the rotate, control of that circuit is compromised when other pilot-pressure demands occur.
  
• Response of Relief inside the Solenoid Valve: Though there is internal relief, if set too high or if the valve is not matched to the flow demand, then rotation may overspeed when other functions reduce the load.
  

Possible Solutions & Recommendations
To resolve or improve performance of the grapple rotate circuit, consider the following:

• Install a Diverter or Priority Valve: A hydraulic diverter or pilot priority valve could ensure that the rotate spool gets a stable portion of pilot flow even when other pilot demands are present.
  
• Use the Option Spool When Available: If the machine has an unused option (auxiliary) spool, tapping into that is often better than running off test ports or jury-rigging from other circuits.
  
• Limit Simultaneous Functions: Training operator to avoid running high pilot load functions simultaneously (e.g., rotating grapple while lifting boom under heavy load) can reduce erratic behavior.
  
• Valve Sizing & Hose Lengths: Ensure hydraulic hoses and fittings to the rotate solenoid are large enough and as short as possible to reduce pressure drop.
  
• Adjust Relief Valve Settings: Possibly adjust relief settings (within safe limits) so that the relief inside the rotate solenoid yields at a pressure appropriate for the rotate motor without being overwhelmed by tank pressure spikes when other circuits are active.
  
• Alternative: Use Swing Circuit: Some suggested repurposing or sharing the swing circuit if the swing function is not used concurrently with rotate; i.e. when rotate is needed, temporarily redirect swing control or stall swing to allow pilot flow.
  

Practical Examples / Anecdotes

• One user tried tapping off a test port to supply the rotate circuit. It worked perfectly when rotate was the only active function. But as soon as the boom or bucket was moved, the rotate motion sped up too much (because the pilot flow had less load) or became erratic.
  
• Another operator installed a diverter valve so that the rotate circuit would have a controlled share of pilot flow, preventing it from receiving "free flow" when other functions reduce their pilot usage; this reduced the over-speed and improved control.
  

Conclusion
On Deere/Hitachi EX150-160 excavators, adding a grapple rotation circuit is feasible, but it must be done carefully. The internal pilot pump location complicates adding extra dedicated pilot supply. To get reliable, safe, and smooth rotate action, the rotate must be integrated in such a way that:

• It shares pilot flow appropriately without taking all when other functions are used.
  
• The relief and control spools are matched to the flow and pressure demands of the attachment.
  
• The hydraulic path (hoses, fittings) is not introducing excessive pressure drop.
  
• Operator practice accounts for the fact that multiple functions reduce available pilot flow.
  

With properly sized valves, possibly priority/diverter valves, and mindful operation, the rotate circuit can work well without negative side effects. If you want, I can help calculate expected pilot flow demands or suggest specific valve models compatible with EX150-5 for rotate circuits.