In contrast to vacuum valves that are actuated by manual (operator turns a handle / lever), pneumatic (an attached air cylinder opens / closes the valve), motorized (a motor drives a screw / shutter), or piloted (a small solenoid stage operates a larger one) operation, a direct acting solenoid valve opens and closes entirely by the electromagnetic force of an attached solenoid. Direct acting valves have the benefit of allowing computerized / automated control of vacuum systems without manual intervention (manual valves) or the need for a compresses air system (pneumatic valves). They will open / close without a long time delay (motorized) or the requirement of a pressure differential (piloted valves); open/close times are typically under 100ms allowing a vacuum system to automatically isolate in the event of a leak or power failure.
Careful selection of valve type is required to ensure suitable conductance in the molecular flow region of the pump down curve; a solenoid valve designed for compressed air use (typically 1/16" orifice) will not have enough conductance to effectively pump down a fusor (though these may be used to vent to atmosphere if suitably leak tight). I have compiled a list of commercially available direct acting solenoid valves designed for high vacuum applications (and their specs) in the attached spreadsheet below, as well as some pictures of these valves to assist in selection of a proper valve for your vacuum system. Note that the prices listed are new prices, eBay prices will be much cheaper. Voltages listed specify 24Vdc when a dc model is available, many are also available in 120/240vac, other flange options are usually also available.
Edwards IPV16EKS
Edwards LCPV16EKA
Varian L9940-306 / Ideal vacuum ElectroMAG
CKD HVB41
MKS ECV16
Pfeiffer EVI 005
Test results of the valves are as follows:
The default configuration was a 2ft KF16 metal flex hose connecting my turbo station to my fusor. The fusor has an Edwards IPV16EKSvalve mounted on the vacuum chamber, this was present on all tests. For some of the tests the fusor was conditioned by plasma cleaning and baking with the vacuum vessel heaters. Several valves were placed between the turbo pump and the flex hose, pump down curves were measured starting with a 10mTorr Deuterium back-fill. Conditioning effects the ultimate vacuum, but not the initial pump down rate. Neutron output (at ~9mTorr operating point) was not affected by choice of valve.
Valves tested by placing in series with existing system were:
Edwards LCPV16EKA
Varian L9940-306
MKS ECV16
Pfeiffer EVI 005
Pump down curves
Close up view
raw data and plotting code in matlab file
An overview of direct acting solenoid valves
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An overview of direct acting solenoid valves
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Re: An overview of direct acting solenoid valves
Thanks Andrew for the test data on the various situations of different valving systems. Valves are very important in amateur vacuum systems. I would rather have great valves in my systems than a great pump. Valves keep things isolated as needed for proper operation and system protection. My three Varian manual valves in fusor IV cost 4 times more than the total that I paid for my mechanical and diff pump combined! It was money well spent.
Fast closing of direct action valves is certainly a very desirable thing to have in large expensive systems. Frankly, I wish I had a fast closing valve in my fore line. We lost power in the midst of a fusor run at HEAS 2016. Fortunately, I wrenched the fore line valve down immediately and then went to the chamber valve, isolating the diff pump. I did it just in time as I did not need to remove and clean the diff pump. (Worked fine once power was restored.) Still, I wish I had a single, direct acting valve in my fore line.
Richard Hull
Fast closing of direct action valves is certainly a very desirable thing to have in large expensive systems. Frankly, I wish I had a fast closing valve in my fore line. We lost power in the midst of a fusor run at HEAS 2016. Fortunately, I wrenched the fore line valve down immediately and then went to the chamber valve, isolating the diff pump. I did it just in time as I did not need to remove and clean the diff pump. (Worked fine once power was restored.) Still, I wish I had a single, direct acting valve in my fore line.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment