Summary of Valve Design Status for nEDM

L. BartoszekBARTOSZEK ENGINEERING

6/20/05

Flow diagram identifying valves

• The following diagram is taken from Steve Williamson’s talk at the Cost and Schedule Review last February

• The system diagram has changed somewhat– A valve (or two?) may have been eliminated– The design issues have stayed the same

Valves (8.2)

• Super-fluid tight cryogenic valves are required to control LHe in purification-injection-measurement cycle

• Low heat load to 0.3 K

• Special materials required in some cases

– Low neutron activation– Must not depolarize 3He or n

• Must be reliable: 100,000 cycles

●Superfluid tight●Low n activation●Must not depolarize 3He●Must not depolarize n

What was in the C&S review:Description of valves and auxilliary components: QuantityWarm actuators 8Feed-through from warm to 4K piston and cylinder 74K piston and cylinder in upper cryostat 74K piston and cylinder on 4K shield near cell or on purifier 7Gaseous He plumbing connecting cylinders 7.3K superfluid-tight, 3He friendly valves 2Large aperture vacuum valve, 4K 1.3K superfluid-tight, 3He & UCN friendly valves 4.3K superfluid tight valve, not friendly to UCN, LHe3 1

This table was taken from WBS dictionary item 8.2.2

There is a discrepancy between this list and the previous system diagram

Only eight valves were costed, there are nine in previous diagram

What are the design issues?

• Making the valves out of materials that are compatible with the polarized He3 and UCNs– All valve materials must be non-magnetic and

valves close to neutrons must not become activated by neutrons

• Getting driving force to the valves– Can’t push on the internal works

• Can’t be a major heat leak

Second order design issues:• Sealing superfluid helium

– There are several designs in the literature and available commercially that seal superfluid helium

– Main issue is adapting the designs with materials compatible with UCNs and LHe3

• Long term sealing functionality– Valve seats must not be damaged in actuation

• Fatigue of moving parts

Where did the actuator design come from?

• I talked to Rich Schmitt from Fermilab• We brainstormed two ideas:

– the “pneumatic” actuator– Actuation by strings (long tension elements)

• I have not been able to figure out how to make the second one work so far

• The thing we liked about the pneumatic design was that the warm driver and the cold valve could be almost completely independent and joined by a simple tube

4K S

hiel

d

300 K actuator

First stage bellows at 4K

300K to 4K transition

Second stage bellows at 4K sized to provide 100 lbs seating force (FNAL experience)

LHe in

LHe out

Superfluid-tight valve seat

4K to 0.3K transition

“Pneumatic” plumbing for gaseous He at 0.75 atm.

Valve springs open when not

actuated

0.3K

Superfluid Valve Operation

Courtesy of Steve Williamson

Important points:• The helium in the actuator must never go

over ~10 psi or it will liquefy• We want to avoid liquefaction because of

the heat given off to the surroundings from the latent heat of vaporization of the helium

• The pressure in the plumbing and in (or around) the two bellows is constant– The pressure changes as the volume of the

system changes

More points:• The force balance on the valve must be

carefully considered because the pressure change is inversely related to the volume change. If the pressure needs to increase by a factor of 10, the volume of the actuator He space needs to shrink by a factor of 10

• This could lead to long stroke first stage bellows since most of the volume change is in the first stage bellows.

Design of the second stage bellows actuator showing the gas volume outside the bellows

Internally pressurized bellows suffer from an instability called “squirm”. I don’t know if it would be significant for a short bellows at only 10 psi. It is possible to design both actuator bellows to see external pressure.

He gas

Jan’s conceptual design for a valve was a good place-holder for the model of the experiment. It shows all the salient features of the needed valve.

Valve Design

Large dead space when valve is open

Commercial superfluid LHe valve from EADS Space

The flow-through path of this valve is more constant in aperture than in the conceptual design.

This appears to be solenoid actuated, so that’s out.

I would use the flow path of this valve, maybe seat design too.

Placement of actuators

• Mounting first and second stage actuator bellows is another challenge of the design

• The following pictures show the second stage actuators for the inlet and outlet valves for one measuring cell

• Primary actuators are assumed to be mounted on the upper cryostat, but can be placed anywhere convenient

These are the inlet and outlet valves for the measuring cell on one side. The green rings are the smallest standard bellows that can deliver 100 pounds of force with 10 psi He gas.

They are 4.25” OD X 3.20” ID.

(Bellows shown are SS)

The second stage actuator bellows are mounted to the 4K shield. The actuator rod penetrates the coils surrounding the measurement cells. The valve bodies are embedded in the central helium vessel wall.

A view with the central vessel rendered opaque and the valve bodies sticking out.

The bellows are interfering with each other because the internal tubes are too close together.

The actuator pushes on the valve seat with 100 lbs of force. That force must be reacted by a tension connection between the actuator and valve body (not shown). The vessel support structure or plumbing cannot react out that force. HEAT!

All the shields and coils visible

valve

bellows

Conclusions I:• I should focus on the design of the valves

nearest the measuring cells because the system diagram has become uncertain far away from the cells

• I see a rational path to final design• It would be good to seal off the sealing

bellows inside the valve when the valve is open to lower the dead space in the valve– Requires 2 way forces – Probably can’t get enough force on the stem

outward

Conclusions II:• We need to finalize the list of materials

acceptable to both polarized He3 and UCNs as soon as possible.

• We will probably have to collect our own fatigue data on non-ferrous bellows actuated at .3K (the ones inside the valve bodies)

• I’ll have to research non-ferrous large bellows for the actuators– May need 4K fatigue data on these

Conclusions III:

• The second stage actuators create big holes in the magnetic shielding.– The impact needs to be evaluated

• Getting everything assembled is going to be very tricky (but you knew that)

• What kind of pressure sensors and gas filling system are needed to fill and monitor the actuators?