Momentary high-pressure surges in a hydraulic system can create noise and may lead to hoses jumping and tubing vibrating. These pressure spikes put a strain on the system and should be minimized as much as possible. They accelerate wear in pumps and motors due to internal bending of shafts and overload on bearings, which can ultimately result in catastrophic failures, such as ruptured lines or broken component housings.
Pressure spikes primarily occur during valve shifting and sudden decompression of oil under high pressure. This discussion will focus on valve-related issues, while decompression shock will be covered in a future issue.
Automotive Lift Repair Orlando 4-way valves are a convenient and cost-effective method for controlling hydraulic cylinders and unloading the pump when the valve spool is centered. However, these valves can generate pressure spikes in the pump line during spool movement.
Automotive Lift Repair Orlando valves are commonly available with special spools that have open porting in the crossover positions, which can help reduce shifting shocks. However, this design may result in increased spool leakage due to a shorter sealing length. In manual valves, operators may drop the load if they hesitate while shifting the spool.
When designing industrial hydraulic systems with solenoid 4-way valves, it is advisable to limit the use of tandem center valves to low-power systems (under 25 HP). For higher-power systems, closed-center valves should be utilized with an appropriate unloading arrangement.
Automotive Lift Repair Orlando Vent-type pump unloading is generally preferred over tandem center valve unloading in industrial hydraulic systems using solenoid 4-way valves for two key reasons:
1. The pressure spikes that occur when the valve spool shifts are virtually eliminated, as high flow and pressure are redirected to the tank through a vented relief valve before the spool reaches the crossover position.
2. Multiple branch circuits can be operated from one pump in a parallel configuration, ensuring full pressure is available to all branches simultaneously. In contrast, tandem center valves must be connected in series, which limits pressure availability across all circuits.
The relief valve serves not only as an adjustable maximum pressure limiter but also as a pump unloader when vented. It should be a two-stage valve (also known as a pilot-operated relief) with an external vent port.
All branch circuits should incorporate 4-way valves with blocked pressure ports to facilitate parallel connections. Various valve types, such as closed center, float center, or 2-position (no center neutral), may be used. The pump is unloaded by venting the pilot-operated relief valve when all branch circuit solenoids are de-energized. When the solenoid is de-energized, the relief valve releases pressure, allowing pump oil to flow to the tank with minimal resistance. Conversely, when the solenoid is energized, the vent line is blocked, and the relief valve resumes its function as a maximum pressure limiter.
For the electrical control circuit, whenever any valve solenoid is activated, a corresponding solenoid must also be energized through a separate set of contacts to load the pump for pressure. Conversely, when all 4-way valves are centered, that solenoid should be de-energized to unload the pump.
Automotive Lift Repair Orlando Cushion relief valves are commonly used across the ports of hydraulic motors to decelerate the motor safely to a stop when the 4-way valve spool is centered or passing through a closed port crossover position. These valves should be non-adjustable and set to a cracking pressure about 500 PSI higher than the maximum system pressure to prevent abrupt stops.
Most Automotive Lift Repair Orlando hydraulic motors should be protected with cushion valves, except in low-speed operations (below 500 RPM) or when the load primarily consists of friction or pure torque rather than the rotation of a large mass.
For applications requiring a softer stop, adjustable cushioning circuits can be implemented. Two cushion relief valves can be set to various degrees of deceleration. Instead of discharging to the opposite motor port, these valves connect to the pump pressure line. Pressure in this line keeps them blocked while the motor runs, but when the 4-way valve spool is centered, the pump line redirects to the tank, enabling effective cushioning.
To prevent cavitation at the motor inlet when oil discharges across the cushion relief valves, a pair of check valves with a low cracking pressure of 3 PSI should be added. These check valves should be plumbed to the tank port of the 4-way valve, taking advantage of back pressure in the tank return line to assist in their operation.
Relief valves for cushioning should be poppet-type (not spool-type) and direct-acting (not pilot-operated) to ensure rapid response to pressure spikes.
Automotive Lift Repair Orlando Pressure compensated pumps typically use a closed center 4-way directional valve. Manufacturers provide data on this, and a miniature relief valve is recommended if the compensator’s response exceeds 100 milliseconds, especially in scenarios with short connecting lines between the pump and the 4-way valve.
Using hose connections instead of rigid plumbing between a hydraulic cylinder and its 4-way control valve can help minimize valve shifting and decompression shocks, although they cannot be completely eliminated.
The primary difference between hydraulics and pneumatics lies in the materials they utilize. Hydraulics use pressurized fluids to facilitate mechanical actions, relying on incompressible fluids—typically oil—to transmit force without volume changes under pressure. As the fluid circulates through the system, the applied force can be amplified significantly, potentially reaching up to nine times the original force. Hydraulic systems generally comprise a network of pistons, with a basic arrangement featuring two pistons. Adding more pistons increases both complexity and force output.
In contrast, Automotive Lift Repair Orlando pneumatic systems operate with gas instead of liquid. They consist of interconnected components through which compressed air flows, supplied by a compressor, and regulated by valves. Similar to hydraulic systems, the compressed air in a pneumatic cylinder is converted into mechanical energy. In some instances, inert gases that do not undergo chemical reactions are employed for specific tasks within pneumatic systems.
– Ease of Control: Operators can start, stop, accelerate, or decelerate processes using a straightforward set of levers and buttons without requiring significant adjustments.