4/23/2013 1 Valves PRESSURE CONTROL VALVES • Relief – Simple – compound • Counterbalance • Unloading • Pressure reducing Protect actuators or Circuit reliefs – Such as a external force acting on a cylinder when the valve is in neutral. • Provide lower pressures – Operate a circuit at a lower pressure than that of the system pressure. FORCE America Inc. RELIEF VALVES • Simple – Noisy, creates heat, high pressure override • Compound – Quiet, low pressure override • Size – Rate by GPM • Location
Transcript
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Valves
PRESSURE CONTROL VALVES
• Relief
– Simple
– compound
• Counterbalance
• Unloading
• Pressure reducing Protect actuators or Circuit reliefs
– Such as a external force acting on a cylinder when the valve is in neutral.
• Provide lower pressures
– Operate a circuit at a lower pressure than that of the system pressure.
FORCE America Inc.
RELIEF VALVES
• Simple
– Noisy, creates heat, high pressure override
• Compound
– Quiet, low pressure override
• Size
– Rate by GPM
• Location
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P T
A B
M
Relief Valves
Load
The relief is set at 1000 psi so it will maintain that pressure
Pressure
Return Pressure
Inlet
FORCE America Inc.
Direct Acting Relief Valves
800 psi
Relief is set at 1000 psi
1000 psi
Relief is set at 1000 psi
Pilot Operated Relief
800 psi
20 psi spring
800 psi
980 psi spring
800 psi + 20 psi spring = 820 psi so the valve stays seated
Pilot Operated Relief
1000 psi
20 psi spring
980 psi
980 psi spring
980 psi + 20 psi spring = 1000 psi so the valve will lift
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P T
A B
M
Load
Counter Balance Valve Sequencing Valve
P T
A B
M
Load
Load
Sequence valve is set at 500 psi
PressureReturn Pressure
Inlet
FORCE America Inc.
PRESSURE REDUCING
• Reduce pressure in a sub circuit
• Designed to let components operate continuously at a lower pressure than the main relief
Pressure Reducing Valve
P T
A B
M
The relief is set at 1000 psi
The pressure reducing valve is set at 500 psi
PressureReturn Pressure
Inlet
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FORCE America Inc.
UNLOADING VALVES
• High– low pump circuits
• Unloads high volume pump at a pre‐determined pressure
• Used in applications where a rapid extension of a cylinder is necessary at a low pressure
• High pressure pump unloads, the low volume high pressure pump takes over
Unloading Valve
5gpm
15gpm
M
Unlading valve is set at 500 psi
The relief is set at 2000 psi
PressureReturn Pressure
Inlet
UNLOADER MID INLET UNLOADER INLET
Load sense signal to V40 section
Power core
Tank core/passageway
Load sense signal to V20 section
Power core
Pilot pressure for solenoid operated sections
Tank core/passageway
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Directional Control Valve
Reservoir
EnginePump
Filter
Directional Control Valve
PressureReturn Pressure
Inlet
FORCE America Inc.
DIRECTIONAL CONTROLS
• Operate actuators in a system
• Two types
• Monoblock
– Single casting, multiple spools
– Least expensive
– Limited to flow and pressure
– No circuit protection available
MONO BLOCK VALVE Sectional ValveSectional valves
•Wide variety of options•Different types of spool actuators
•Open or closed center applications•Power beyond capabilities
•Allowing fluid to be used down stream of valve
•Sections can be added •Load sensing•High flows and pressures available•Relief valves can be built into them
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Add-A-Fold® Valve
Typical valve assembly
Shuttle valves,
1 per section
Manual override connection
SPIN‐A‐VEYER SECTION
The valves have manual overrides which are the red knobs on the proportional coil, turning the red control knob clockwise will start the section to flow.
In‐line Check Valve Pilot Operated Check – Pilot to Open
M
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The common practice is to use pilot operated to‐open check valves to hold static loads and to use counterbalance valves to hold dynamic loads. For example, aerial lifts include both the man lift boom as well as outriggers, which steady the lift frame. The outriggers, are held in position by pilot operated check valves while the man lift boom is commonly held in position by an over center valve. The boom is a dynamic load in that it is moved frequently, while the outriggers are set and remain stationary during operation of the aerial lift.
Pilot operated check valves (one way directional control valve)Pilot check valves will hold a load in position, but their operation is not as smooth as that of counterbalance valves in throttling the flow as the load is lowered. Pilot operated to‐open check valves do have the advantage of locking the load in position because the check valve has a positive seat, where spool type counterbalance valves will have some leakage. Both counterbalance valves and pilot operated to‐open check valves are mounted in or close to the cylinder port with rigid plumbing.
PILOT OPERATED CHECK VALVES
A single selector valve is used to operate two‐control valve from a single pump or two single acting cylinders with one directional control valve.
The multiple selector vales allow additional functions to be operated with a single pump source.
SELECTOR VALVES
A P B T A P B T
A P B TA P B T
Closed Center Float Center
Open Center Tandem Center
Valve Center Options
P T
A B
P T
A B
P T
A B
P T
A B
Parallel Circuit
100 psi
200 psi
300 psi
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Series Circuit
100 psi200 psi300 psi
Page 157
2 Stage Directional Controls
PA BT
2 Stage Directional Controls
PA BT
Energize the solenoid and the valve will shift
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FORCE America Inc.
FLOW CONTROLS
• Designed to regulate the speed of a cylinder or motor
• Non compensated– Used in circuits where load pressure remains relatively constant and feed rates are not critical. Any change in the workload would affect the flow or speed of an actuator. A needle valve or fixed orifice are examples of non compensated controls.
• Compensated– Adjust the flow as the load increases or decreases according to the induced load. The flow will remain constant no matter what load does.
FORCE America Inc.
FLOW CONTROLS
• By‐pass type
– Maintains flow required by means of an adjustment, the unused fluid is diverted back to the reservoir
• Restrictor type
– Maintains flow of an actuator
– In‐line with the actuator
– Restricts the flow, unused flow is dumped over the relief valve
– Can cause high heat build up
FLOW CONTROLS• Designed to regulate the speed of a cylinder or motor
• Non compensated– Used in circuits where
load pressure remains relatively constant and feed rates are not critical. Any change in the workload would affect the flow or speed of an actuator. A needle valve or fixed orifice are examples of non compensated controls.
