Mechanically Actuated Valves
– This valve is a two-position, four-way, spring-offset type, actuated mechanically rather than manually.
– It features a spool end with a roller, typically operated by a cam mechanism.
– The graphic symbol remains the same, but mechanical actuation is shown with a circle representing the cam-driven roller, instead of manual.
For a deeper understanding of the complete functionality of the hydraulic valve, please continue to read the following essay. Remember that if using this essay to perform your own DIY work on a hydraulic cylinder, that you always consult the manufacturer’s manual and regard any and all safety precautions. Please contact a trained professional technician if you have any questions!
Pilot-Actuated Valves
– Springs at both ends of the spool push against centering washers to keep the spool centered when no air is applied.
– Air pressure introduced through the left end shifts the spool to the right, while air through the right end shifts it to the left.
– This type is a four-way, three-position, spring-centered, air pilot–actuated directional control valve, with dashed lines indicating pilot pressure lines.
Automotive Lift Repair Florida Solenoid-Actuated Valves
– Solenoids are a common method for actuating spool valves. Energizing the solenoid coil generates a magnetic force that pulls the armature, moving the valve spool.
– Solenoids are mounted on the valve housing, and a cutaway view shows the solenoid-actuated directional control valve.
– Solenoids act on a push pin, which is sealed to prevent oil leakage. There are two solenoid designs for heat dissipation:
– Air Gap Solenoid: Dissipates heat into the surrounding air.
– Automotive Lift Repair Florida Wet Pin Solenoid: Contains an internal passage for tank port oil, which better dissipates heat by circulating oil to the hydraulic system.
– The fluid around the armature cools and cushions it, avoiding seal wear and reducing friction. This design eliminates impact loads that can cause solenoid failure.
– This valve is equipped with a solenoid at each end of the spool and is a solenoid-actuated, four-way, three-position, spring-centered directional control valve.
– Three-position valves can have various flow path configurations.
– Each four-way valve has the same actuated flow path but different spring-centered paths:
– Open-Center Type: Connects all ports, allowing pump flow to return to the tank at atmospheric pressure and enabling the actuator to move freely with an external force.
– Closed-Center Type: Blocks all ports, using pump flow for other circuit parts and locking the actuator connected to ports A and B against external movement.
– Tandem Design: Locks the actuator and unloads the Automotive Lift Repair Florida pump at atmospheric pressure. Unlike the closed-center type, it avoids high-pressure pump flow, reducing wear and extending pump life.
Shuttle Valves
– Shuttle valves are directional control valves that enable operation from two fluid power sources.
– They are used for safety, allowing a secondary backup pump to operate if the main pump fails.
– The shuttle valve consists of a floating piston that shifts depending on which side has greater pressure.
– It can be spring-loaded to favor one supply source or unbiased, with the flow direction determined by circuit conditions.
– Essentially a direct-acting double-check valve with cross-bleed, shuttle valves permit reverse flow as indicated by the double arrows on the graphic symbol.
Pressure Control Valves
Simple Pressure Relief Valves
– The pressure relief valve is the most commonly used pressure control valve, found in nearly every hydraulic system.
– A poppet, held in place by a stiff compression spring, is pushed off its seat when the hydraulic force exceeds the spring force as system pressure rises.
Pressure-Reducing Valves
– The pressure-reducing valve is designed to maintain a reduced pressure in specific areas of a hydraulic system.
– This normally open Automotive Lift Repair Florida valve is actuated by downstream pressure and closes as this pressure approaches the valve setting.
– If downstream pressure is below the valve setting, fluid flows freely from the inlet to the outlet.
– An internal passageway transmits outlet pressure to the spool end opposite the spring, causing the spool to move and partially block the outlet port when the pressure reaches the set point.
Unloading Valves
– Unloading valves allow a pump to build pressure to an adjustable level and then discharge oil to the tank at nearly zero pressure as long as pilot pressure is maintained from a remote source. This minimizes the load on the pump, resulting in minimal power consumption.
– Unlike pressure relief valves, which operate at full pump flow and pressure, unloading valves maintain a near-zero pressure while still delivering full pump flow.
Sequence Valves
– Sequence valves control the operation of a hydraulic system in a specific sequence.
– When the components connected to port A reach the valve’s adjusted pressure, the valve allows fluid to pass through port B for additional work elsewhere in the system.
– The high-flow poppet of the sequence valve, controlled by a spring-loaded cone, blocks flow at low pressures. Flow through port A is restricted until the pressure reaches the preset value.
– Once the pressure at port A reaches the set value, the main poppet lifts, allowing flow to port B. The valve maintains the pressure at port A until the pressure at port B equals the pressure at port A.
– A small pilot flow then goes through the control piston and past the Automotive Lift Repair Florida pilot cone to an external drain. When pressures at A and B equalize, the control piston seats, halting pilot flow loss, and the main poppet opens fully to allow both pressures to rise together.
Counterbalance Valves (CBV)
– The primary port connects to the bottom of the Automotive Lift Repair Florida cylinder, while the secondary port connects to a directional control valve (DCV).
– The counterbalance valve’s pressure setting is slightly higher than the load weight, ensuring the cylinder doesn’t fall.
Flow Control Valves
– An Automotive Lift Repair Florida orifice can function as both a flow meter and a flow control device by measuring the pressure drop (Δp) across it. For a given orifice, there is a unique relationship between (Δp) and Q (the flow rate through the orifice).
– This relationship can be described by an equation that relates Δp to Q, allowing for accurate measurement of liquid flow rate through the orifice.