Internal Pilot Operated Valves

Internal Pilot Valves

Similar to 3500, 3505, 3510, 35KR, 4500, 4600, 4700 Series

This type of valve is provided with a 2-way pilot solenoid operator. A diaphragm or piston provides the seal for the main seat. These solenoid valves are used for switching pressures in conjunction with orifice sizes larger than those available with direct-acting valves.

The floating diaphragm construction requires a pressure drop across the main valve seat to remain in the open position, or a coupled diaphragm or piston which is mechanically held open by the solenoid plunger (i.e. Chem-o-sol). The coupled type will operate with zero pressure drop across the main valve seat.

An Internal Pilot Operated 2-way valve is shown in Fig. 6. When the solenoid is energized, the plunger opens the pilot orifice and relieves pressure from the top of the diaphragm to the outlet side of the valve, through the pilot channel in the main body. This results in an unbalanced condition which causes the main line pressure to lift the diaphragm off the main seat, thereby opening the valve. When the solenoid is de-energized, the pilot orifice is closed and full line pressure is applied to the top of the diaphragm, through the bleed orifice located in the diaphragm, from the inlet side of the valve, thereby providing a seating force for tight shut-off. As long as a pressure differential exists between the inlet and outlet ports, a residual shut-off force is available by virtue of the larger effective area on the top side of the diaphragm.

In most cases an internally piloted valve will require a minimum line pressure to insure sealing of the main orifice. This is due to the fact that the diaphragm is usually produced in a flat fashion and is made of some type of elastomeric material which will have a tendency to pull the diaphragm back to its normal position.

Figure 6:—