BCIT: Millwright Level 3 (Hydraulics: Valves 1)

What type of valve controls the speed of the actuator?

The speed of an actuator is controlled by a flow control valve (FCV).

What type of valve controls the force of an actuator?

The force of an actuator is controlled by a pressure control valve (PCV).

Which five (5) pressure control valves are normally closed?

Relief, counterbalance, unloading, sequence, and brake valves are normally closed

Which pressure control valve is normally open?

Which pressure control valve is normally open?

Which valve is the first valve downstream from the pump in a hydraulic system?

The first valve downstream from the pump is the maximum pressure relief valve (Maximum PRV).

Who should adjust the maximum pressure relief valve?

Only qualified personnel should adjust the maximum pressure relief valve.

List four (4) ways to unload a pump.

A pump can be unloaded by venting the relief line, using a pilot-operated unloading valve, installing an on/off valve to tank from the pressure line, or using an unloading valve.

What happens if you do not provide a pilot drain on a sequence valve or a pressure-reducing valve?

If a pilot drain is not provided, the valve may not operate correctly after a few cycles.

What happens if you install a brake valve on a motor without connecting the pilot to the inlet?

If the pilot is not connected, the motor will not turn.

What three (3) types of elements are used in directional control valves?

Directional control valves use poppet, sliding spool, and rotating spool elements.

What is meant by a way in a valve?

A way in a valve refers to the path through which fluid flows.

List two (2) ways to use a three-way, two-position directional control valve.

A three-way, two-position directional control valve can be used as a diverter valve or to operate a single-acting cylinder.

What is the purpose of the pilot chokes on a directional control valve?

Pilot chokes control the shifting speed of the spool in the directional control valve.

How are valves held in their normal positions?

Valves are held in their normal positions by springs.

What three (3) types of spool centres could you use to allow the cylinder to float?

Open center, float center, or motor center spool configurations allow the cylinder to float.

What are the three (3) flow control methods?

The three flow control methods are meter-in, meter-out, and bleed-off.

Do pressure control valves control the speed or the force of an actuator?

Pressure control valves control the force of an actuator.

What is the main purpose of a maximum pressure relief valve?

The main purpose of a maximum pressure relief valve is to set and limit the pressure in the system.

What is the purpose of an unloading valve?

An unloading valve depressurizes the system before the maximum pressure relief valve opens.

Would you use a normally open or a normally closed valve to relieve the pressure in a system?

A normally closed valve is used to relieve the pressure in a system.

What can happen if you set the maximum pressure relief valve above the maximum pressure for which the system is rated?

Setting the maximum pressure relief valve above the system rating can cause serious equipment damage or personal injury.

What is pressure override?

Pressure override is the difference between the cracking pressure of a valve and the pressure required to pass full flow through the valve.

What is the purpose of venting the relief valve?

Venting the relief valve allows the system to be unloaded from a remote location.

Would you use a normally open or a normally closed valve to reduce the pressure in a branch of a circuit?

A normally open valve is used to reduce pressure in a branch circuit.

What happens if a particle of dirt gets caught between the poppet and seat of the reverse flow bypass on a pressure reducing valve?

If dirt gets between the poppet and seat, the valve may not be able to adjust flow or maintain the correct cracking pressure.

Would you use a normally open or a normally closed valve to control the sequence of an operation?

A normally closed valve is used to control the sequence of operations.

If the second cylinder in a sequence circuit fails to move after the first cylinder completes its stroke, which troubleshooting technique should you try first?

The first troubleshooting step is to decrease the spring setting on the sequence valve.

Which pressure control valve can be used instead of a counterbalance valve?

A sequence valve can be used instead of a counterbalance valve.

What happens if dirt gets between the poppet and seat of the reverse flow bypass on a counterbalance valve?

If dirt gets between the poppet and seat, the load may move freely.

Should you connect the pilot from a brake valve to the inlet or the outlet of a motor?

The pilot can be connected externally to the supply or internally to the pump outlet depending on the design.

Can you operate a double-acting cylinder with a three-way, two-position directional control valve?

No, a double-acting cylinder cannot be operated with a three-way, two-position directional control valve.

Which type of spool centre do you need if the cylinder must be locked when the spool is centered and pump flow must return freely to tank?

A tandem center spool is used in this situation.

What happens if someone shuts off the pilot chokes?

If the pilot chokes are shut off, the main spool will not shift.

How can you check to determine whether the pilot solenoids are working?

You can manually shift the spool to check whether the pilot solenoids are functioning.

What kind of spool do you need to increase the extension speed of a cylinder?

A regenerative spool is used to increase the extension speed of a cylinder.

What kind of check valve do you need if you want to have a minimum pressure loss in the valve?

A right-angle check valve provides minimum pressure loss.

What kind of check valve do you need to lock a double-acting cylinder when the directional control valve spool is centered?

A pilot-to-open check valve is used to lock a double-acting cylinder.

What kind of check valve do you need to automatically drain an accumulator when the pump is shut down?

A pilot-to-close check valve is used to automatically drain the accumulator.

Does a flow control valve control the force or the speed of the actuator?

A flow control valve controls the speed of the actuator.

What is the safest flow control method if the cylinder is used for a steady lift with the rod extending?

Meter-in flow control is the safest method for this condition.

Which flow control method provides the best control when the loading is unsteady?

Meter-out flow control provides the best control for unsteady loads.

What is the danger of using meter-out flow control on the rod end of a cylinder if the load pulls on the rod?

This can create a pressure intensifier condition.

What kind of flow control provides the greatest energy efficiency?

Bleed-off flow control provides the greatest energy efficiency.

Where should you locate a flow control with a reverse flow bypass to control the actuator speed in both directions?

It should be located upstream from the directional control valve.

What kind of flow control valve allows speed control in one direction and full speed in the other direction?

A flow control valve with a reverse flow bypass allows this operation.

What is the purpose of a pressure compensator on a flow control valve?

A pressure compensator maintains stable flow when the load changes.

What is the purpose of a temperature compensator on a flow control valve?

A temperature compensator maintains actuator speed when the fluid temperature changes.

What is the purpose of the overspeed control feature on a flow control valve?

The overspeed control feature prevents the actuator from moving too quickly when the spool shifts.