The advantages of the solenoid-pilot design are high flow capability, reliability and low power consumption. The disadvantage is that it requires a minimum pilot pressure to shift the valve plunger. The advantage of a direct acting solenoid is that there is no minimum pressure requirement. The disadvantages are limited flow capability and high power consumption.
Force is required to shift a pilot or solenoid-pilot valve. The shifting force must overcome the opposing force (often a spring holding the valve in one position.) The valve specification includes a minimum force required to force the valve to shift. The physical force achieved by a pneumatic valve is created when the pressurized media acts on the surface area of the pilot piston, creating force. The force is measured by the pressure (of the media) multiplied times the surface area on which the pressure is applied (F=P x A). The minimum pilot pressure is minimum amount of pressure required to create a force greater than the opposing force in the device, thus allowing the control device to function.
In a direct acting valve, the main body or poppet is moved using magnetic force from the electricity to shift the valve. In a solenoid-pilot operated valve, the main body or plunger is moved using force developed from the available main body pressure. The small solenoid is used just to control the pilot piston.
A solenoid-pilot directional control valve utilizes a combination of a direct acting solenoid and a pilot valve. The solenoid direct acting valve controls the flow of a pressured media going to the pilot valve. The pressurized pilot media pushes on the pilot piston which creates a force (F=P x A). That force is used to move the plunger in the pilot valve. Flow control occurs via the configuration of the plunger. The action of moving the plunger controls the flow of the media. The advantages of the solenoid-pilot design are high flow capability, high reliability, low power consumption and simplicity of piping/installation as pilot lines are integral to the valve. The disadvantage is that it requires a minimum pressure to shift the plunger.
Direct acting solenoid valves are used to control the flow of fluid and gas media. The most common types of flow control are opening, closing, selecting different media or diverting a media. A direct acting solenoid flow control valves shifts via an electric coil. When energized, it creates a magnetic field that moves a metal poppet. The direct action of energizing and de-energizing the solenoid controls the flow of the media, turning it on and off. The advantage of a direct acting solenoid is that there is no minimum pressure requirement. The disadvantages are limited flow capability and high power consumption.
Expilot is a term used to describe a solenoid-pilot directional control valve utilizing an external pilot signal. A pilot signal, often referred to as the pilot pressure, creates the force required to do work in the main body pilot valve. Solenoid-pilot valves utilize an internal or an external source for its pilot signal. An internal pilot source utilizes the main body media as the source of the pilot signal. A valve that uses an external pilot source does not utilize the main body media rather requires a separate, external pressurized source for the pilot signal. An expilot design is common when the pressure of controlled media does not meet the minimum pressure requirement of the main valve or where the control media need to be separated from the main body media.
Versa patented the Anti-Extrusion Principal which is an O-ring sealing arrangement we invented for our valves. O-ring seals offer great advantages in valve design. They make valves rugged and reliable and are simple to assemble and maintain. Because there are readily available standard and custom O-ring seals, there is a wide choice of sealing materials, which is all great news.
However, when O-rings are used as a dynamic seal sometimes the internal forces can cause the seal to move or jump. When this happens the seals can become extruded or “nipped” which leaves small defects on the seal material. Our Anti-Extrusion Principle offsets the disadvantages of using O-rings by using a patented sealing arrangement in our O-ring packed valves. Basically, Versa seats O-ring seals within the valve body or on the valve plunger so the flow of the media or the pressure differential through the valve helps seat the O-ring. This keeps the O-rings in place which reduces the risk of extrusion and thereby enhances valve performance and life.