Steam hammaring 1

If there's a temperature control valve on the steam supply to the heat exchanger (and there almost always is) hammering can occur at low loads if the condensate system isn't arrange correctly. As the temp control valve throttles in, you have exactly the same thing occuring as if you had a pressure reducing valve. The steam pressure falls in the heat exchanger, and with it, the available differential to push condensate across the trap orifice. The other thing that can occur, is if the condensate from this heat exchanger is tied into a line that is shared by other equipment, then the back pressure on the heat exchanger trap can vary. This will also affect the heat exchanger.

To eliminate hammering, the condensate from the heat exchanger needs to gravity drain to a vented condensate receiver. A vacuum breaker should also be installed on the steam side of the unit to allow drainage when the steam valve shuts completely.

If you can get a copy of Spirax Sarco's book "Hook-Ups", it has all of this information, and much more. It's a thin, soft cover publication that contains a huge amount of information, and I highly recommend it.

Small correction, it is degrees "celsius" not centigrade Steven van Els
SAvanEls@cq-link.sr

Hello,

Another small "nit" to pick.

You are not experiencing "steam hammer" but rather hot water "flashing" to (some) steam (but mostly vapor) and "bubble collapse" when the steam goes back to liquid phase ("bang&quot. Steam hammer occurs much the same way liquid hammer does. Steam hammer does not involve phase changes - there is only steam in the line. Similarly, Liquid (e.g., water) hammer involves pipes FILLED with water - no air is involved. When a "slug" of water (e.g., condensate) is propelled down a steam pipe it is not "water hammer" but rather "slug flow". These are commonly confused issues.

I concur with TPB in his comments.

Regards, John.

"Steam hammer occurs much the same way liquid hammer does. Steam hammer does not involve phase changes - there is only steam in the line."

Ummm, I'm no fluid dynamics expert, and I might be wrong, but I thought that the pressure transient (the wave/pressure discontinuity that causes the hammer event) can be caused by several different things, one of which is in fact rapid phase change, e.g. rapid condensation/vapor collapse of steam in a water line? I once saw a 12" cogen main steam header jump clear out of its pipeway when they hit the header with warm water on unit startup. Pretty dramatic, to say the least... Broken anchors, guides, that sort of thing... Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com