Blowdown Valves

A blowdown vavle is used in air compressors. When the unit reaches capaciry it blowsdown, Also on units that are computer controlled when they are going to shut down they blowdown first to relieve the pressure in the seperator tank prior to shutting down. As for an itermittent valve I don't know these.

Another use of a blowdown valve is to prevent the compressor from stalling and drawing heavy current if you start it against full pressure.

So they add a valve to the line from the comressor to the tank that vents to the air when the power is off. When the power is on it closes the valve and pressure goes to the tank with the pump starting from ambient. There is also a one way valve going into the tank

In steam applications :

Internittent blow down valve is mounted at the bottom of the steam boiler and is used for blowing out the accumulated sediments ,by opening at a constant time intervals (Like once every shift)

Continuous blow down valve is mounted about 100 mm below the low water level of the steam boiler and is continuously blowing out boiler water , thus causing fresh feed water to enter the boiler and maintaining a constant disolved solids amount in the boiler water. This function is crucial for the elimination or ,more accurately,reduction of the amount of sediments.

A very similar application can be met also in cooling towers systems.

One must also remember that Total Dissolved Solids [TDS] are removed from a boiler by blowdown as well as the selltable solids. The purer the feed water, the less frequent the blowdown needs to be. If the TDS in a boiler is too high, then the bolier will "prime", i.e. liquid will be carried over into the steam. Priming can introduce safety concerns: were the boiler to be attached to a set of superheaters and thence to a railway locomotive's driving wheels, there would be a significant delay between shutting the regulator and the locomotive's power output reducing. Beware all buffer stops..

Have you heard about Emergency shutdown valve, in that according to process condition the valve need to shutdown in order to product the process from any disaster or to make the system safety. Now the blowdown valve, this you can see in the equipmant lines like exchanger, compressor etc. to product the equipment from abnormal conditions like overpressure build up or any other possiblities of equipment blew up.This valve lead the fluids to flare header.