Hydraulic Symbols

HYS102

Part D

Pressure Control Valves

{sounds of throat clearing}

Beginner’s Series

Please advance each slide at the tone.

Advance Search Forward & Reverse

1. Each member of the pressure control family starts with a square

2. Yes, good job. The 2 little lines are the ports

3. Add an arrow to indicate the flow path thru the valve

4. Add a dashed line from the inlet port to the top of the valve

5. Add a spring, and while you’re on a roll, put an arrow thru the spring at a 450 angle

1. Excellent! We have a relief valve

2. The flow path arrow is not in alignment with the ports3. Which

means the valve is normally closed

5. Until pilot pressure in the dashed line is high enough to overcome the spring force

4. The spring holds the valve closed

6. Yon 450 arrow means that the spring, and thereby, the pressure setting of the valve, is adjustable

What have we learned so far?

1. A relief is one member of the pressure control family

2. The valve is held in its normally closed state by the spring until the pilot pressure exceeds the spring setting

3. The arrow thru the spring shows that the spring is adjustable

1. A sequence valve symbol is the same as a relief with the addition of an external drain

2. Typically, a sequence valve is used to cause one cylinder or motor to start moving before another cylinder or motor Sequence Valve

1. the counterbalance valve symbol is the same as a relief

2. Typically, a counterbalance valve is used to hold a load from falling

Counterbalance Valve

What have we learned so far?

4. A Sequence valve has an external drain

5. A counterbalance valve symbol is the same as a relief valve

1. A brake valve symbol is the same as a relief and includes an external pilot line in addition to the internal pilot line

2. Typically, a brake valve is used to brake the speed of a freewheeling hydraulic motor

Internal pilot

External pilot

Brake Valve

1. An unloading valve symbol is the same as a relief, but it has external pilot

2. Typically, an unloading valve is used to unload a pump at low pressure

External pilot

Unloading Valve

1. The pressure reducing valve is the only normally open pressure control2. Typically, it’s used to reduce the pressure in a portion of the system

Pressure Reducing Valve

3. It has internal pilot, but this silly thing has it coming from the outlet port

4. You know an external drain when you see one

5. This valve, as well as most of the others, comes with an optional check valve

Normally open

What else have we learned?

6. A brake valve has both internal and external pilot lines

7. An unloading valve is like a relief except it has an external pilot line

8. A pressure reducing valve is wierd

the only Normally open pressure control

Pilot pressure sensed from the outlet port

Thanks for hanging with me

Close this window and click on the final module, then you’re done

Wanna hook all of these valves up? There’s hands-on training in Birmingham