Introduction
The solenoid valves can be classified as Direct acting solenoid valves and servo assisted in this session we are gonna breifly discussed about the servo assisted valve anatomy and Different types of servo assisted valves.
Servo Assisted Valve Anatomy
Pilot Valve
Pilots can use any of the direct acting principles (plunger, pivot, rocker or flipper) to provide either isolated or non-isolated actuation which, in turn, governs the applicability of the whole valve. The pilot armature can assist without physical connection to the main seal or can be mechanically connected with a spring or hard coupling method to aid further in the opening when there may not be enough differential pressure across the valve.
Chamber
Pressure is equalized in the chamber and is the space into which the diaphragm or piston recedes to allow flow.
Pilot channels
Allow fluid to move out of the chamber and from the pilot to downstream to enable the fluid to assist in opening the
main seal.
Equalization hole/channel
Allows pressure to slowly equalize between the inlet and the chamber above the diaphragm or piston to seal the valve. This hole is replaced by a channel when an isolated 3/2 pilot is in place. Above the seat flow All servo assisted valves use above the seat flow and have very low back-pressure resistance.
Spring
The spring works with the fluid to revert the valve back to its normal position when the pilot valve sees no power. In
valves which are subject to chemically aggressive fluids the spring is omitted allowing only the fluid to close the valve.
Main Orifice
The area on which the media pressure will act and the gap through which the media will flow when the valve is
energized. Along with the contours of the valve it governs the pressure drop and the flow rate of the valve.
Fluidic Connection
Many fluidic sizes and connections are available to meet local geographic or industry specific standards.
Seal
A soft material, either a diaphragm or a flat seal attached to the underside of a solid piston or a plunger which halts the flow of fluid from one side of the main orifice to the other.
Seat
A raised area on the orifice which concentrates the pressure of the seal. In some cases the seat is made from a more
abrasion resistant material than the body material.
Different types of servo assisted valves
1.Servo Assisted: Diaphragm (Plunger Piloted)
This operating method uses a direct acting plunger valve as the pilot valve and the main valve seal is a flexible diaphragm. The fluid chamber above the diaphragm is relieved when the pilot opens. The medium pressure beneath the diaphragm lifts the diaphragm and opens the valve allowing flow. When the pilot valve is closed, the medium pressure is allowed to build up again above the diaphragm through its small equalizing orifice and closing is aided by the force of the compression spring.
2.Servo Assisted: Piston (Plunger Piloted)
This operating method uses a direct acting plunger valve as the pilot valve and the main valve seal located on the base of a solid piston which moves vertically through a cylindrical chamber. The fluid chamber above the piston is relieved when the pilot opens. The medium pressure beneath the piston lifts the piston and opens the valve allowing flow. When the pilot valve is closed, the medium pressure is allowed to build up again above the piston through the equalizing orifice in the piston body and closing is aided by the force of the compression spring
3.Servo Assisted: Spring Coupled
Like other servo assisted valves, these spring coupled valves take advantage of the fluid’s pressure to operate. The addition of a direct soft mechanical coupling between the main diaphragm or piston and the plunger of the pilot armature means that there is some extra assistance. This linkage is especially useful in the case of low pressure differentials, where the coupling allows the valve to start to open without differential.
As in the case of all servo assisted valves the pilot is responsible for opening the channel between the chamber and the downstream port allowing the pressure in the chamber to sink and thus the path can be opened for flow to occur through the main orifice. When the power to the pilot is removed the design also ensures slow, water-hammer free closing and tight shut-off.
4.Servo Assisted: Hard Coupled
Like spring coupled valves, hard coupled valves can take advantage of the fluid’s pressure to operate – but the addition of a direct and solid mechanical coupling between the main diaphragm or piston and the plunger of the pilot armature means that there is a much more dominant direct acting force component.
This direct and solid linkage can be employed where there is zero pressure differential as the strength of the coil acting on the coupling can open the main valve without aid. When the power to the pilot is removed the design also ensures slow, water-hammer free closing and tight shut-off.
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