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| Hydraulic
Valve >> Hydraulic
Check Valves |
 The
non-return valves or check valves are used to block the reverse flow
of oil or gas in a fluid power circuit. Additionally this valve may
be used for pressure control or directional control. The check valve
consists of a valve body with inlet and outlet ports and an internal
movable member biased by the spring. The movable member can be a flapper
or a plunger but most often in valves of hydraulic systems, it is
a ball or poppet. They are built to provide free flow in one direction
and a check in the other direction and prevent flow-back in hydraulic
systems.
Check valves
are of several styles: swinging disc, ball, plunger, and
poppet. Check valves of the pilot-operated type are also popular.
The connection at the bottom is connected to a remotely operated pilot
valve, As in the ordinary check valve, free flow is permitted in one
direction when the line pressure lifts the plunger thus opening the
valve. The flow is checked in the opposite direction until pilot pressure
is applied to the blind end of the plunger through the pilot connection.
This causes the plunger to unseat the valve spool and oil is allowed
to flow through the valve.When system pressure at the check valve
inlet port is high enough to overcome the biasing spring force on
the poppet, the poppet is pushed off its seat allowing oil to flow
through the valve. This is known as the check valve's free flow direction.
When the fluid attempts reverse direction of flow, the spring pushes
the poppet back on the seat to block flow through the valve. Check
valves can be direct acting or pilot operated. A pilot operated version
is used where the no-flow characteristic of the valve is desired only
for a portion of the system cycle. A pilot operated check valve also
allows free flow from its inlet port to its outlet port just as in
an in-line check valve. The design and construction of a check valve
makes it one of the simplest fluid power components. Though simple,
its use can make the system sophisticated. By application of check
valves one can also design many sophisticated circuit diagrams where
a constant flow can be maintained in both directions by using them
in a bridge.
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