Power Purge - air removal
#1
01-02-10, 02:59 PM
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Power Purge - air removal
Here is a piping scheme for implementing a power purge for air removal from a heat emitter:
Power purging can be helpful for hard-to-bleed systems - such as heat emitters below the main or barely above the main, or for lines with low points in the middle.
To purge, first cool down the boiler to 100 deg (to prevent flashing to steam and thermally shocking the boiler by injecting cold make-up water into a hot boiler). Open the isolation valve ahead of the automatic fill valve - a.k.a. pressure reducing valve - (on the connection to the boiler from the city water supply). This replaces the water as it is purged from the system.
Shut the return valve and open the hose bib. (The supply valve is optional - it isn't needed for purging.) Full-port ball valves give a higher flow rate and better air removal. Best to connect a short piece of hose from the bib into a bucket with a few inches of water - so that you can observe any air bubbles removed. 30 seconds or less of purging should be plenty adequate for most situations.
Restore the valve lineup, but leave the automatic fill valve's shut-off open for a day or two for system pressure to recover.
You may already have sufficient valving in your system to accomplish a power purge - for either a single heat emitter or a whole zone - without adding any valves. Purging in the direction of normal flow is ideal, but if you are constrained by existing valving, you can try purging backwards.
Power purging can be helpful for hard-to-bleed systems - such as heat emitters below the main or barely above the main, or for lines with low points in the middle.
To purge, first cool down the boiler to 100 deg (to prevent flashing to steam and thermally shocking the boiler by injecting cold make-up water into a hot boiler). Open the isolation valve ahead of the automatic fill valve - a.k.a. pressure reducing valve - (on the connection to the boiler from the city water supply). This replaces the water as it is purged from the system.
Shut the return valve and open the hose bib. (The supply valve is optional - it isn't needed for purging.) Full-port ball valves give a higher flow rate and better air removal. Best to connect a short piece of hose from the bib into a bucket with a few inches of water - so that you can observe any air bubbles removed. 30 seconds or less of purging should be plenty adequate for most situations.
Restore the valve lineup, but leave the automatic fill valve's shut-off open for a day or two for system pressure to recover.
You may already have sufficient valving in your system to accomplish a power purge - for either a single heat emitter or a whole zone - without adding any valves. Purging in the direction of normal flow is ideal, but if you are constrained by existing valving, you can try purging backwards.
Last edited by Mike Speed 30; 01-02-10 at 03:24 PM.
#2
01-03-10, 12:25 PM
I started working on a drawing to illustrate this a while back, but never finished it... yours is simpler than mine and perhaps easier to follow.
THanks! let's hope we can find this thread again when we need it!
THanks! let's hope we can find this thread again when we need it!
