The pilot valve regulates the discharge of fluid to adjust the main valve spool or poppet, ensuring that the flow through the main valve aligns with the demands of the reduced pressure circuit. When the low-pressure circuit no longer needs flow, the main valve closes. Any high-pressure fluid that seeps into the reduced-pressure section is then redirected to the reservoir through the pilot-controlled relief valve.
Sequence Valves
In Automotive LIft Repair Florida hydraulic systems with multiple actuators, it is common to operate components such as hydraulic cylinders in a specific sequence, often determined by the load each cylinder needs to handle.
Space limitations and force requirements usually dictate the appropriate cylinder size. Sequence valves can be used to ensure that cylinders are activated in the correct order.
Automotive LIft Repair Florida Sequence valves are typically closed 2-way valves that control the operational sequence within a circuit. While they resemble direct-acting relief valves, their spring chambers are usually externally drained to the reservoir, unlike relief valves which drain internally through an outlet port.
Sequence Valve
A sequence valve is designed to direct pressurized fluid to a secondary path only after the primary path or task is completed. In its default closed position, the Automotive LIft Repair Florida valve allows hydraulic fluid to flow to the primary circuit until the preset pressure level is reached. Once the primary function is achieved, the pressure increases and acts on the spool, overcoming the spring force. This compression shifts the spool, redirecting hydraulic fluid to the secondary circuit.
Counterbalance Valves
Normally closed counterbalance valves maintain a specific pressure in part of a hydraulic circuit to counteract weights or external forces, such as in a hydraulic press, preventing uncontrolled free fall. The main port connects to the rod end of the hydraulic cylinder, while the secondary port connects to the directional control valve. The valve is set to a pressure slightly higher than necessary to prevent the load from falling freely.
The Automotive LIft Repair Florida counterbalance valve blocks fluid flow from its inlet port to the outlet port until the pressure at the inlet port exceeds the spring force. When pressurized fluid enters the hydraulic cylinder cap, it extends the cylinder, raising the pressure at the rod end. This increased pressure shifts the main spool in the counterbalance valve, allowing fluid to flow through the secondary port to the directional control valve and eventually to the reservoir. The check valve opens during lifting to allow the cylinder to retract freely.
Counterbalance Valve
To boost cylinder force and alleviate backpressure at the bottom of the stroke, counterbalance valves can be remotely controlled. Typically, they are internally drained. During extension, the valve opens its secondary port to allow fluid to flow to the reservoir. When retracted, the check valve ensures the spool remains unaffected.
Unloading Valves
Automotive LIft Repair Florida Unloading valves are used to offload pumps by regulating the pump’s output flow—usually from a standalone pump in a multi-pump system—directly to the reservoir at low pressure once the system reaches its set point.
The valve remains closed due to spring force. An external pilot signal must exert sufficient force on the opposite end of the valve spool to overcome the spring force and shift the spool, redirecting the pump output to the reservoir at reduced pressure.
Piloted Unloading Valves
Piloted unloading valves feature a pilot control for the main valve. They include a port through the main valve plunger, allowing system pressure to act on both sides of the plunger.
The valve stays closed due to the combination of a light spring and system pressure acting on the larger surface area at the spring end of the plunger.
A built-in check valve maintains system pressure. When the pressure drops to the set point, the pilot valve closes, causing the flow from the pump through the port in the main valve spool to close the valve.
Directional Control
Automotive LIft Repair Florida Directional control valves manage the flow of fluid by directing it into one or multiple paths, whether from several sources or a single source. A spool inside the valve determines which paths are open or closed. Directional control valves can be operated either electronically or manually.
Solenoid Directional Valve
Directional control valves have three main functions:
1. Stop fluid flow
2. Allow fluid flow
3. Change the direction of fluid flow
These functions often work together.
Types of Directional Control Valves
The main types include:
– Two-way, three-way, and four-way valves
– Check valves
– Solenoid-actuated valves
The most common is the 2-way valve, which either allows or blocks fluid flow, similar to a water tap.
A single-acting hydraulic cylinder requires a 3-way valve to supply and exhaust fluid. Some 3-way valves also have a third position to block flow.
A 4-way valve is needed for double-acting actuators, independently pressurizing and exhausting two ports. A 3-position, 4-way valve can also stop the actuator or allow it to float.
Check Valve
Automotive LIft Repair Florida Check valves are 2-port valves with one port for fluid entry and the other for exit. They come in various materials, including polymers, metal, and rubber, and can have swing or flap designs, or use spring and ball mechanisms.
Check valves typically remain closed due to spring force. When fluid pressure exceeds the cracking pressure, the ball or disc moves away from its seat, allowing flow.
Duckbill Check Valve
Duckbill check valves use a rubber diaphragm that keeps the valve normally closed unless positive pressure is applied. Unlike metal check valves, they are highly reliable, immune to seizing, rusting, or binding, and less prone to mechanical wear.
Solenoid Valve
Solenoid-operated directional valves control the opening, closing, or redirection of fluid flow. They use a solenoid—an electrically powered coil around a ferromagnetic core—to actuate a spool that opens or closes ports.
Key Considerations for a Solenoid Valve
– Number of ports and positions
– Spool positioning and action
– Flow requirements
– Material compatibility
– Temperature tolerance
– Pressure endurance
Hydraulic Cartridge Valves
Cartridge valves manage the pressure, direction, and flow of hydraulic fluid internally. These inline valves operate parallel to the fluid flow and are ideal for high flow rates and effective leakage control.
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