Depressuring Solenoid Valve

Few ideas:

1. two valves interlocked when 1 closes the Nitrogen off, the number 2 opens the system to relief the trapped pressure

2. a two way valve. Regular the vent is closed, when valve operates it opens the system for pressure relief and closes the inlet. Not sure if those can operate with Pressure from both sides.

3. contact vendors of Solenoid valves. You have not stated the pressure in the system, but you might be looking at specialised stuff here.

Caution: Nitrogen vented into closed space is dangerous and further precaution has to be taken to vent it off to open space.

Thanks for your thoughts. I have thought down those paths too. I'm just trying to reduce the system complexity. If I can avoid using multiple solenoids I will. A two way solenoid seems to be the solution. I will have to discuss with the manufacturer it's pressure capabilities (in the order of 1500 PSI) and movement of the shuttle when high pressure exists on both sides.

Thanks.

Maybe not in your case, but ordinarily there is a downstream pressure regulator on gas cylinders. If so, the solenoid may see pressures like 50-100 psi, which is easily managed. Some solenoids permit reverse flow when deenergized, and you'll need to avoid that if using a 3-way type.

Any 3/2 solenoid valve configured air-to-open/spring-close with the appropriate pressure, voltage and frequency characteristic would do it.

Make sure that the vent port of the solenoid valve is connected to the same place as the venting arrangements around the cylinder to as to prevent the air in the neigbourhood of the test bench becoming nitrogen-rich/oxygen-lean.

Contact ASCO with your specifications.They probably have a stock valve to handle your situation.

Link: www.ascovalve.com

Why nitrogen and not -40degC dewpoint instrument air? It would be rather less hazardous.

...and if the test can be performed using water instead of nitrogen or air, that would be even less hazardous.

"High Pressure" is an ambiguous term.Please be more specific.

Standard ASCO RedHat Solenoid valves are good up to 200 psi and are rated for air,and inert gases.

A 3way valve would suit your purposes,with a muffler, or restricter orifice, fitted to the exhaust port, or connect it to an isolated discharge location.

Connect your cylinder under test to the common port,and your pressure source to the normally closed port.The exhaust from the cylinder under test will be via the normally open (de-energized) port.

If power to the solenoid is interrupted by a power failure, or an E Stop switch, the cylinder will bleed off through the open port.

Simple.

"High Pressure" in this case refers to the cylinder pressure without an integral cylinder regulator. BOC gasses state that thier cylinders are supplied at approximately 25000Kpa. From the research that I've already done, (including with ASCO) there is no direct acting 3 way solenoid valve that can handle a DP of 25000Kpa.

There are more complex apparatus that will meet this requirement, but I was hoping to avoid them. In hindsight I think I will use a regulator on the cylinder as the highest foreseeable calibration pressure I will require is 6000Kpa.

The reason I have chosen nitrogen as opposed to water or air is purely for logistical reasons. The instrument air is supplied at a maximum of 700Kpa and water is supplied at 400Kpa. I try to avoid using instrument air on apparatus that contains or has contained hydrocarbons, to avoid enriching the mixture of combustible vapours. It's inert, non corrosive and suits this purpose fairly well.

Hopefully I won't cause anyone to asphyxiate! Any N2 vent will be outside of any occupancy and leaks should be detected by the O2 sensors and regular maintenance of course.

Here is a link to as ASCO engineering Guide.

http://valvesandinstruments.com/pdf/ASCO_Engineering_Guide_20061108.pdf

I wasn't involved in the selection process, but I believe Nupro valves were used. e.g. http://www.swagelok.com/search/find_products_home.aspx?show_results=Y&item=1693af08-4a08-41c4-9319-f2364e816b9b

The cylinders were in explosion proof vented cabinets with sprinklers (N2 was a purge gas). Initially we used an excess flow valve and an electric valve attached directly to the cylinder. After a failure of an excess flow device we changed to an air operated valve and an orifice. The added benefit for us was if there was a fire, the plastic air tubing would hopefully melt. The primary reason for changing to an air-operated device was because the electric valve wasn't UL listed and inside the gas cabinets in what could be under a fault condition an explosive atmosphere.

Air may make the system easier to design and you probably would want to vent through a metering valve or an orifice. Nearly all connections were VCR.

Some of the Nupro air actuated valve did have status switches, although not the ones we used in the cabinets, The regulators were on the backing plates in the cylinder cabinets.

The system was also tripped by the fire alarm.

Automatic shutdown systems for use on chlorine cylinders do precisely the task you require. Also suitable for Nitrogen, oxygen and exotic very expensive gasses like volatile perfume oils. Try Chlorguard.com. (manufactured by PSI Global Limited who have an agent in Australia)

How much flow do you need? If you can use 1/4"BSP connections & 4.7mm dia flow holes, Thompson Valves in England make a 2-way solenoid valve that works up to 4000psi. This can be connected in either energise-to-open or energise-to-close mode. In either case the downstream service will be vented when the inlet is disconnected. The vent port is also threaded, so the vented gas can be piped away from the operating area.
You can connect the Solenoid downstream of the Bottle Regulator as suggested. This is like having a filter downstream of the Regulator; you will have to compensate for any pressure drop incurred, by manipulating the Regulator setting.

Drew

Re-reading my post: the term '2-way solenoid valve' is misleading. It actually has 3 ports and operates as a change-over valve.

Drew

An ASCO 3 way solenoid valve will work.

Be sure to vent the exhaust away from the work area.

http://www.ascovalve.com/Applications/Products/SolenoidValves.aspx

Thanks for the directions. I'll check out the manufacturers suggested and see if they suit my purposes. All the input is appreciated.

We used to use these at NASA up to 2000 psi.

http://www.marotta.com/fluid-control-building-blocks/solenoid-valves.html