Solenoid valve costs cut with moulded polymers

Edited by the Engineeringtalk editorial team Aug 15, 2000

Peter Paul Electronics, New Britain, Connecticut, USA, has improved product- performance and reduced manufacturing costs for its Series 40 solenoid-operated valve using DuPont engineering polymers

Peter Paul Electronics, New Britain, Connecticut, USA, has improved product- performance and reduced manufacturing costs for its Series 40 solenoid-operated valve.

According to the company, this development was a blank sheet approach to producing less expensive valves, using DuPont engineering polymers for injection moulded parts and encapsulation.

The redesigned valve is engineered for competitive cost and reliable service in humidifiers, pneumatic automation systems, beverage dispensers and other equipment.

The valve's main components are a solenoid assembly, a valve body and a plunger.

When the solenoid coil is energised, a spring-loaded elastomer-tipped plunger is drawn away from an integral seat in the valve body, allowing fluid to flow through the unit.

The new valve's solenoid assembly is encapsulated with Rynite PET thermoplastic polyester resin.

Its coil bobbin is injection moulded from Rynite PET or, for food or beverage equipment, DuPont Delrin acetal resin.

The valve body is injection moulded from Delrin .

Prior to this design, encapsulation was done with thermoset epoxy, and the valve body was metal.

Existing valve lines use thermoset epoxy encapsulation and the bodies are made of machined brass, stainless steel, or aluminium.

"In switching to Rynite for encapsulation, Peter Paul got much shorter cycles, eliminated VOC (volatile organic compound) emissions from epoxy and eliminated secondary finishing," says Tom Pellegatto, Senior Design Engineer for Peter Paul.

The strength and mouldability of Rynite also allowed the integration of a support bracket into the encapsulation.

Another key feature of the new design is the use of the inner diameter of the bobbin to guide the valve's plunger.

This eliminates a precision-welded metal assembly incorporating a nut, a guide sleeve for the plunger and an end stop.

A cylindrical metal end stop, which limits plunger travel, is now insert-moulded in the encapsulation.

Tolerances for end stop positioning are much closer with the new design, +/-0.002 in (51 �m) instead of +/-0.005 in (127um), which helps assure consistent valve operation.

For the injection-moulded body, Delrin provides the strength, stiffness and dimensional stability required to replace machined metal.

With Delrin , the body also has a smooth, attractive surface.

Valves have operated without failure for 20 million cycles with water and air at temperatures from 0 to 49C.

They are available with orifices from 0.8 to 3.2 mm and are rated for service pressures up to 17.2 bar.

For pneumatic control applications, a three-way version is made with a port at the top to exhaust air from downstream cylinders when the valve closes.

The solenoid meets UL 1446 Class F (155C) requirements.

Peter Paul met this requirement by selecting a pre-approved, pre-tested DuPont electrical insulation system (EIS) incorporating Rynite 415HP and FR530.

The availability of the EIS for the Rynite PET resins saved a good deal of time and testing expense.