|
|
| Indirectly solenoid actuated |
|
| |
These valves operate according to the differential pressure or pilot
principle (servo principle) and make use of the pressure energy of the
operating fluid to open and close the valve seat. The pilot system functions
as a booster, so that even with a solenoid of lesser magnetic force (than that
of directly actuated valves) fluids flowing at high rates under high pressures
can be controlled.
(Both pistons and diaphragms are used as sealing elements for the main seat).
Description of function:
Valve closed (Fig. 1)
The solenoid is de-energised and its core (pilot valve piston) closes the vent
(pilot seat). The upstream pressure in P (greater than the downstream pressure
in A) builds up through the bleed orifice in the diaphragm (2 bleed orifices
in the piston) on the top side of the diaphragm (or piston).
This pressure, multiplied by the area of the top of the diaphragm (or piston)
produces a closing force which is greater than the opening force exerted on the
diaphragm (or piston). It is forced onto its seat.
|
| |
|
Fig. 1
|
|
Solenoid de-energised
|
| |
| |
|
|
| |
Valve opens (Fig. 2)
The solenoid is energised. The magnetic force, greater than the closing
force exerted on the core (spring and pressure force), raises it from the
vent. This relieves the pressure in the space above the diaphragm (or piston)
and a balance of pressure with the A-side of the valve is achieved. This
pressure relief continues, as less fluid can flow through the bleed orifice
than can escape through the vent.
Thus the opening force, resultant from the higher upstream pressure in P on
the diaphragm (or piston), is greater. This is raised from the valve seat and
the valve remains open as long as the prescribed pressure differential remains
between P and A. Depending on the type of valve this is between 0.5 and 1 bar.
|
| |
|
Fig. 2
|
|
Solenoid energised
|
| |
| |
|
|
| |
Valve closes
The solenoid is de-energised and the core closes the vent by means of the
spring and pressure force. Above the diaphragm (or piston) the same pressure
as on the P-side builds up again, and the resultant force pushes the diaphragm
(or piston) onto the valve seat.
The flow direction of the fluid is fixed.
|
|
