Poppet or check shut off valves
Pressure relief valve simulation
Leak free sealing of flow in one direction.
Allows flow in only one direction.
Provides positive back pressure on a system when fitted with a spring.
Also used as simple low pressure relief valves.
Fixed spring to control the opening or cracking pressure
Fit valves without springs vertically
Pilot operated – can be opened by pilot pressure to allow flow back through valves.
Can be used as leak free directional valves. Typically for low flow, high pressure situations or for very high flows where directional valves are expensive or not suitable.
Directional control valves
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Flow control accuracy can vary widely between valves.
Pressure reducing valves
Maintains the downstream pressure in a circuit.
Can only reduce system pressure not increase it.
Pilot pressure - Changes in pilot drain or backpressure can effect the pressure setting.
Pilot or direct operated
Backflow capability - Some systems require backflow capability in case downstream pressures go up as well as down.
Pilot operated - controls setting remotely.
Proportional control valves
Proportionally control the flow into the A or B lines depending on the angle of a hand leaver or value of electrical control signal.
Also available as proportional relief and reducing valves.
Proportional valves require a significant pressure drop across the valve to accurately control the flow, say 30 bar.
Require good fluid cleanliness
Require suitable electrical control cards
Manual or electrical operation.
Spool centre leakages vary depending on free flow path or pressure venting.
Pilot or direct operated valves. Low flows generally direct acting, large flows piloted.
Valve response times may vary.
Control pressure drop across valve to give repeatable flow accuracy independent of system.
Servo directional control valves
Very accurately control the flow into the A or B lines depending on the electrical control signal. Generally used in high performance closed loop control systems.
Servo valves require a significant pressure drop across the valve to accurately control the flow, say 30 bar, and stiff, high natural frequency, systems to operate correctly.
Require very good fluid cleanliness
Spool centre positions bias may vary.
Valve response times may vary.
Hydraulic Cylinder Parts
Hydraulic cylinders derive power from hydraulic fluid. The various parts of the hydraulic cylinder are cylinder barrel (which is actually a piston connected to a piston rod), a separate barrel which is closed on each end with a cylinder bottom, and with a cylinder head and rod gland. Let's have a look at various hydraulic cylinder parts in detail.
* Cylinder Barrel: The cylinder barrel is the area where the piston makes back and forth moments. The barrel is a unlined thick walled pipe that is situated inside the cylinder. The cylinder barrel is perfected internally.
* Cylinder Head: Cylinder head is connected to the barrel with a lock or screw. Most engineers say that a flanged connection should be used to connect the head and barrel. Flanged connections are ideal, but they cost a lot. The advantage of having a flanged connection is they are always simple to remove for maintenance and other purposes.
* Cylinder Bottom: The barrel and bottom portion are welded together in most hydraulic cylinders. In most cases this damages the inside of the barrel if done poorly. However many upcoming new cylinders have a screwed connection from the cylinder end cap to the barrel,...