Pilot operated relief valves use a pressure balanced spool that is controlled by a pilot seat. They provide much greater flow capability for a given cavity size.
Direct vs Pilot Operated Valves
Direct: Simple, robust but flow limited. Can see benefits of poppet geometry (secondary lift area) at higher pressure settings.
Pilot Operated: Main spool is normally pressure balanced via sensing orifice. Once valve setting is reached, ball unseats and pressure is relieved from back of spool, allowing valve to open. Allows compact design due to small pressure area on pilot seat.
High flow capability
Easy to adjust
How does pilot operated relief works?
Relief Valve Typical Applications
Main System Relief
Sub System Relief
Pump and Motor Protection
Over Load Protection
Over Torque Protection
Mechanical vs Hydraulic Damping
Kickdown Relief Valve Structure
Initial operation as pilot operated relief valve
Valve opens completely when extra spool drillings open to extra head drilling
Reseats only when inlet pressure < return spring load (~2 bar)
In situation where pressure must be dumped completely once valve relieves, a kickdown valve can be used. E.g. where achieving the relief setting indicates that an unsafe situation has occurred, machine jam, overload, etc.
Kickdown relief valve working principle is as below:
Ventable Relief Valves
Additional port 3 giving great flexibility.
External control of spool balancing chamber pressure
Permits great flexibility of performance
Ventable Relief Valve Usage
Port 3 connected to Proportional Relief Valve
Main setting controlled by Proportional Valve
Retains high flow capacity of pilot operated spool
Port 3 connected to normally closed solenoid valve
Solenoid de-energised, valve setting normal
Solenoid energised, valve unloads pump
Could use normally open solenoid valve to protect pump on start up.
Pilot Operated Relief Valve
Excellent flow / pressure drop performance coupled with extremely low leakage poppet design, and also incorporating reverse check. It can be used in load holding applications.
How to adjust hydraulic pressure relief valves?
PED Cat IV Compliant Valves A04B2Y & A04J2Y (CE marked)
Pressure Equipment Directive 97/23/EC
Where does it apply?
Vessels above specified pressure / volume levels
Accumulators >1 liter and >50 bar-liter
Applies to any safety equipment associated with qualifying systems
What does it mandate?
Fully documented design verification and validation
Fully traceable manufacture
Regular external audits to maintain approval
Key Features / Benefits
Hardened working parts for maximum durability. (with differential hardness between mating parts)
4:1 minimum Ultimate Tensile Strength Factor of Safety
Springs rated to 10,000,000 cycles (Infinite life)
Valves rated to 1,000,000 impulse & cyclic duty cycles
Wide adjustment range in single valve
Wide range of functions available
Flows up to 400 l/min. Pressures up to 450 bar.
Commonality of parts
CE Marked (Complies Pressure Equipment Directive (PED) 97/23/EC)