Bent Axis Piston Motors

Component Related Documentation

Bent axis piston motors are classified as rotary actuators and closely resemble bent axis piston pumps in construction. However, instead of pushing on the fluid as the pump does, the fluid pushes on the internal surface area of the motor, developing torque. If enough torque is available to move the load, the motor shaft will rotate. Bent axis piston motors require an external case drain line in order to prevent failure of the shaft seal due to high case pressure in the event of backpressure on whichever port is the active exhaust flow port. Bent axis piston motors have a two section shaft. The two shaft sections are at an angle to each other, hence the term “bent axis.” This angle causes the pistons to reciprocate in the bores of the barrel which is splined to one shaft section. As the fluid causes the barrel to rotate, power is delivered from the barrel shaft section to the output shaft section.

Safety Related Notes

Before working on this machine, perform lockout-tagout procedures per the rules of your plant. Determine the sources of energy on this machine – electrical, pneumatic and hydraulic – and release or vent sources of stored energy – electrical capacitors, air receivers, and hydraulic accumulators. Shut off sources of power – electrical, pneumatic and hydraulic. Safely block mechanical sources of energy such as loaded springs and loaded machine members, or safely position the machine members so they are unloaded and springs are not under tension. Beware of hot hydraulic fluid and hot surfaces which can cause burns. Never “crack a hydraulic or pneumatic fitting” to check for the presence of stored energy. Hydraulic fluid injection injuries, as well as injection injuries from many other fluids, are extremely serious and must be treated immediately by medical personnel familiar with this type of injury. Loss of body parts or death may result from improperly treated fluid injection injuries! Never use your hands to feel for a hydraulic leak! Review the schematics and think before proceeding to work on the machine to ensure you have made the machine safe to work on.

Troubleshooting Document

Probable Cause	Possible Remedy
External brake needed	Consider the addition of a brake all hydraulic motors have internal leakage allowing load drift.
External brake failure	Check out the cause of the brake or failure.
Load binding	Check for linkage and/or other misalignment. Loosen and retorque motor mounting bolts.
Open brake, crossover make-Up or system relief valve(s)	Check for any all pressure control valves bypassing fluid to tank. Re move repair and/or replace valve(s)
Low operating pressure	Check system pressure, make necessary adjustments.
Motor displacement	Set adjustments to proper motor distributors
Pump not delivering proper volume and/or pressure	Refer to Pump Troubleshooting section.
Seized motor parts.	Disassemble, repair or replace parts. Replace motor.
Piping incorrect from directional control valve	Check piping drawing and correct
Wiring or directional control valve incorrect.	Check wiring diagram and correct.
Incorrect valve spool (tandem instead or motor)	Disassemble, remove and exchange spools Change valve
Inlet oil is hotter	Check for problem at pump (See Pump Troubleshooting section) Wrong viscosity oil Check oil coolers for obstruction or insufficient cooling capacity. Check for low oil level.
Motor slippage too high	Disassemble, inspect motor elements: replace if worn or damaged.
Drain line restricted	Remove and replace
High GMP flow rate	Reduce pump output Readjust flow control valve.
Motor-load coupling misaligned	Realign motor and load coupling to within .005 in TIR
Motor running away	Add flow control to outlet. Reduce load
Aeration	Check for foaming oil. Flush, clean & refill system with fluid having anti-foam additives
Cavitiation	Reduce motor speed. Check viscosity of fluid. Too high, change to fluid recommended by motor manufacturer. Preheat fluid. Check for restricted inlet. Check for open brake, crossover or make-up valve. Check hydraulic pump for cavitations.
Case drain restricted	Check drain line, remove and replace.
Sticking vane (on vane motors)	Disassemble, clean and reassemble Check for proper vane positioning.