EHC System Failure – United Servo Hydraulics Inc.

What causes EHC System Failure?
How does Degraded Fluid Impact System Performance?
What is this damage doing to the EHC components?

Causes of Failure

United Servo Hydraulics is dedicated to minimizing the risk of unscheduled forced outage due to EHC component failure through periodic component refurbishment.

The majority of EHC Component Failures result from:

Wear over extended service periods
Hydraulic Fluid Degradation
Contamination

As service time increases, component wear caused by fluid degradation and contamination accelerates the risk of failure and increases the financial impact.

Costly unit shutdown time due to obstructed system performance.
Increased cost of compenent refurbishment due to the need to parts replacement.

System Performance Impact

The Impact of Degraded Fluid on EHC System Performance

Silt and varnish deposits cause hydraulic valves to stick
Improper flows through orifices
Electrochemical erosion of servo valve parts
Excessive wear and premature failure of main pumps
Clogged pressure line filters

Inside Your Components: Damaged Parts

The Electrohydraulic Control System is heavily impacted by the under-maintained components. The implications often go unnoticed until visible signs of high leakage, loss of control from an unresponsive servo, and valve sticking occur.

Take a look at the internal signs and consequences of wear and degraded fluid over periods of time.

Control Valve Actuator Components

Piston Rod Rust & Scoring

The piston becomes worn and rusted with clear indication of chroming being worn away. Scoring is evident as a result from the wear.

Rod Gland Scoring

Scoring and varnish are visible inside the rod gland, impacting the seal seat and fluid leak-by.

Cylinder Barrel Wear

Deep scoring of the barrel and shoulder restricting piston stroke are evident in this image.

Broken Piston Head

Severe wear on the piston head results in additional system contamination from debris.

Jet Pipe Style Servo Valve Components

Servo Valve Filter Contamination

The state of the servo valve filter gives insight into the condition of your EHC fluid. The photo below shows contamination beyond the normal amount when in service during the OEM specified repair cycle.

Servo Valve Nozzle Erosion

The images show the nozzle within the servo valve torque motor. The torque motor in diameter is .011” and visibly etched and eroded.

A visibly etched and eroded torque motor

Servo Valve Nozzle Erosion

Servo Valve Receiver Port Erosion

The bushing and sleeve assembly’s receiver port shows visible signs of erosion following exposure to contamination.

Servo Valve Receiver Port Erosion

Nozzle/Flapper Style Servo Valve Components

Servo Valve Filter Contamination

The state of the servo valve filter gives insight into the condition of your EHC fluid. The photo below shows a new filter compared to those with normal and high levels of contamination.

Servo Valve Feedback Wire Assembly

The feedback wire assembly shows signs of pitting and varnish on the nozzle flat. The nozzle spacing is .0015”.

Servo Valve Feedback Wire Assembly