Functional description of the Herschel liquid helium valve.

			Functional Description 1 Valve armature housing 2   Upper and lower pole shoe 3   Permanent magnet 4   Solenoid 5   Wiring 6   Valve cap 7   Armature 8   Spring assembly 9   Limit stop with guide 10   Guide spindle 11 Valve poppet 12   Valve seat 13   Upstream and downstream filter. 14   Downstream housing. 15 Indicator housing 16   Reed switch 17   Wiring

Functional description.

The Herschel liquid helium valve is an electromechanically actuated, bi-stable latch valve. Helium shutoff is achieved with a ball-poppet and polymeric seal for internal leak tightness.

Bi-stability is realised by a permanent magnet 3, generating the open and closed holding and sealing force of the valve in absence of an electrical command.

Valve actuation from the 'closed' to 'open' position, and reverse, is performed by an electric command to the solenoid 4, who's magnetic field overrides the magnetic field of the permanent magnet. Preloaded springs 8, move the armature 7, together with the guide spindle 10, and the valve poppet 11, from the lower limit stop 9, to the upper limit stop 1, (top of valve armature housing) or reverse. As the armature approaches the limit stops, it becomes influenced by the magnetic force of the activated solenoid and/or the permanent magnet. This additional influence causes further pre-loading of the springs upon contact of the ball - poppet 11, with the valve seat 12, when the armature is in the fully closed end position. Similarly for 'opening', upon contact of the spring retainer with the upper limit stop when the armature is in the fully open end position. The differential stroke between contact of the ball - poppet and seat and the contact of the armature and lower limit stop is important for the generation of the seat force and the internal leak tightness.

The Herschel liquid helium valve incorporates an external position indicator to show the 'valve open' position. The position indicator comprises a reed switch 16, which is activated the moment the armature comes into contact with the upper limit stop - causing the valve cap 6, to become magnetised.

The individual switching behaviour of the valve is verified by detecting the current variation versus the switching time of the valve.

	Actuator Assembly
	Valve flow elements
	Position indicator
	Views of the valve
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