Usage
Older style belt drive and some direct drive pumps can have oil migration back toward a system if power is shut off to the pump and the system is at vacuum.  These valves segregate the system from the pump if there is loss of electricity to the pump.  People employ these to assure proper shut down of the system or just as assurance of system integrity from power outages,  The solenoids can be controlled using electricity which opens up a wide range of usages including controlled processing of vacuum levels, automating system start up and shut down.  We can tie these valves off of a programmable logic controller (PLC) or a digital acquisition card in the back of a PC.  There is a ton of available control software out there that can run this type of function.

By installing a solenoid on a system and using a manually adjustable valve on top of the solenoid, it is possible to have a pressure bleed to another pressure.  We have used this setup for testing pump operation at varying pressures and controlling the change to these varying pressures.

Solenoids come in varying voltage configurations and frequency for just about any requirement.  Explosion proof housings are available.  The bodies come in either brass or stainless steel.  They use an elastomeric diaphragm which is pushed up or down to seal the vacuum.  The whole contraption is leak tight and uses electro-magnetism to power the functioning of the piston up and down to open and close the valve arrangement.  The valves come in either an normally open or normally closed configuration.  

Standard implementation is to tie a "normally closed" valve into the power supplied to the motor that drives the pump.  When electricity is cut off to the pump the valve closes.  The valve is piped in between the intake port of the pump and the system piping as close to the pump as is physically possible.  Sometimes we tie a "normally open" valve vented to atmosphere between the normally closed valve and the pump inlet.  This then vents the pump inlet to atmosphere when the normally closed valve closes.  This helps maintain pressure equilibrium between the pump inlet and atmospheric pressure.

These types of valves are a poor choice as pressure valves as they can stomach very little back pressure (only held by electromagnet) and should really not be considered for this function.

As you may have seen, by combing the use of electric solenoid valves with vacuum gauges employing an output, it is possible to control many aspects of vacuum pressure and availability of that pressure to the system.