Hydraulics Flashcards
A fixed displacement gear pump is diagnosed with low oil flow in a hydraulic system. Which of the following would likely be responsible for reduced oil flow from the gear pump?
A) Excessive back pressure in the tank
B) excessive internal pump wear
C) pump rpm has been too high
D) relief valve setting set too high
B….. Normal wear over time cause the pump gears to wear the thrust plates on the sides of the pump housing. These are often replaceable on many types of gear pumps. As increase in the end play of the gears is a sign that the pump needs replacement or needs to be rebuilt. Neither increased back pressure nor a higher operating rpm would cause bad appreciable increase in pump pressure will not affect pump wear greatly although wear was present in the pump; the amount of bypassing oil would increase with a higher operating pressure.
A technician is testing a loader with an open centre hydraulic system for proper operation. What will occur to the pump outlet pressure when the control valve is placed in the neutral position?
A) hydraulic pressure increases immediately
B) low pressure will increase slightly
C) oil flows to the tank, pressure decreases
D) actuator return pressure increases
D… when a priority flow is required to a designated circuit before feeding a secondary circuit, a priority compensated flow control can be used to accurately split the flow between the circuits. When it is required a set restriction provides the priority side with a set flow rate to the circuit. As flow rate changes, the secondary circuit will receive more or less flow while the priority side remains satisfied
A tech is checking the operation of a priority flow control valve on a loader. Which of the following should he check first?
A) ensure min pressure in the secondary circuit first
B) check to insure both circuits are fed at the same time
C) ensure max pressure in the secondary circuit first
D) ensure the primary circuit is supplied before the secondary circuit
When a priority is required to a designated circuit before feeding a secondary circuit, a priority compensated flow control can be used to accurately split the flow between the circuits. When it is required, a set restriction provides the priority side with a set flow rate to the circuit. The remaining oil is directed to the secondary circuit. As flow rate changes, the secondary circuit will receive more or less flow while the priority side remains satisfied
A technician checks the bladder type accumulator pressure on a loaders brake circuit and finds the gas charge pressure is too high in the accumulator. Which of the following could result from this condition?
A) excessive brake pressure will occur in the wheel end
B) lower hydraulic pressure will occur in the system
C) damage to the poppet assembly and/ or the bladder
D)greater oil volume will be stored in the system
C… the correct gas pressure-charge pressure must be maintained for proper functioning and optimum service life for a gas charge bladder type accumulator. In a bladder type accumulator, excessive pressure charge can drive the bladder into the poppet assembly during discharge, causing damage to the poppet assembly and/or the bladder
After a tech replaces a single acting telescoping hydraulic cylinder on a drill rig, which of the following procedures must be performed before the equipment is returned to service?
A) air must be bled from port relief
B) air must be bled at the main control valve
C) air must be bled from the telescoping cylinder
D) air must be bled from the hydraulic pump first
C… a single acting telescoping hyd cylinder isn’t self bleeding so that any air trapped in the cylinder must be removed. The port relief valve, control valve and the hydraulic pump don’t need to bled as they are self bleeding in normal operation allowing oil and air to flow through each component
A tech is diagnosing a suspected hyd system low pressure problem. Which of the following criteria must be met before proceeding?
A) start and operate the equipment at low idle for 10 minutes
B) ensure that the hyd oil cooler is bypassed
C) test that hyd pump isn’t leaking internally
D) check that the hydraulic system is a normal operating temp
D… the oil must be up to its normal operating temperature to ensure a correct reading. In cold temp climates this is even more important as the oil viscosity thickens when the temp is below freezing. If there was internal wear in the hyd pump, checking it at below operating temperatures might conceal internal wear due to thicker oil at below operating temp
A tech finds that the boom circuit of a loader drifts down on occasion. Which of the following would likely be responsible for this?
A) leak at the rod end of the dump cylinder
B) intermittent sticking of the main relief valve
C) the dump/hoist control valve sticking
D) Excessive wear to the hyd pump gears
C.. control valves generally have extremely tight clearances between the spool and body. If the problem is intermittent, a quick check of the spool travel is in order. If the spool doesn’t self center itself each time it is returned to neutral, it maybe sticking, causing the load to drift down on occasion
