Flash Steam Vent condenser hammer 1

I would guess that the problem lies in the piping between the receiver and the condenser. It is strange that the steam and condensate pipes are the same diameter. Do you know what the flowrate of steam to the condenser is, and what is the diameter of the steam line?

It also sounds strange that the condensate return line from the condenser is connected to the top of the receiver. You don't want steam trying to go up the condensate return line, and the easiest way to prevent this is to connect it below the liquid level in the receiver.

Please give more details on the piping between the condenser and receiver, specifically describing what measures have been taken to prevent steam going up the condensate line, and to prevent condensate coming down the steam line.

Thanks very much for your reply. The piping does seem suspicious in that when I'm looking at it I wonder how does the steam "know" which line to travel up to the condenser. As far as I can tell no provisions had been made to distinguish the steam supply from the condensate return. The condensate receiver is a cylindrical, horizontal tank, 108" long by 54" diameter approx. The condenser is approx. 8 feet long & shell od is 10.5". the shell nozzle are on the bottom & approx. 6' apart. the nozzles on the receiver are on the top & 17" apart. The vertical height between the bottom of the condenser nozzles & the top of the receiver nozzles is approx. 36". Both lines are 4" od. One line is 78" long (has three 90 deg elbows) & the other line (that connects to the nozzle closest to the tubesheet end) is approx. 98" long (also has three 90 deg elbows).

Greg,

Thanks for the extra info. It is hard to say whether the pipe sizes are adequate from the info that you have supplied, but making a few assumptions I would say that 4" is not far wrong for the steam. The condensate line could be smaller, but being the same size is not a problem.

If cold condensate is returning down a line that has hot steam going the other way hammer is a definite possibility. So I would say the first thing to do is to make sure one line sees only steam, and the other sees only condensate.

Firstly, there should be some means at the condenser to ensure that condensate goes back down only one nozzle. There may be an internal riser (extension) on one of the condenser nozzles to force the condensate down the other nozzle. I hope you have access to a drawing to confirm this. If there is no internal riser, you could achieve the same thing by sloping the condenser by about 2 or 3" to ensure the condensate runs down to the condensate nozzle. If the condenser is already sloped, make sure the lower connection is used for condensate return.

Now that we have got a means to ensure that the condensate runs down the correct line we need to stop the steam coming up the same line. As I mentioned previously, this is usually done by connecting it below the water level in the receiver. It may be easier to simply install a U-leg seal of about 3' in the condensate return line to create a positive seal.

The steam line must be installed in such a way that no pools of condensate can form in it. There must be no low points. Ideally it should be sloped as steeply as possible from the receiver up to the condenser. There will be some condensation in this line and you want the condensate to be able to run out. The shorter this line can be, especially any horizontal runs, the better.

Unfortunately the only way to be sure whether this is the true cause is to make the changes and see if it helps! If there are any similar receiver/condenser installations that do not hammer compare them with the problematic one and note all the differences.

Hello Katmar,

We checked the condenser & it is sloped so we made up a length of pipe with a vanstone on one end and inserted it through the tank nozzle, at the lower end of the condenser, so the end of the pipe extends down near the bottom of the receiver ensuring it will be below the water level (& the vanstone gets clamped in the existing bolted flange along with the gasket).
Therefore, we believed that both of the requirements that you suggested (getting the condensate to only one exit & ensuring steam can't come back up the same line that condensate is going down)were achieved.
We started up last week with this modification and the problem is cured. We were able to shut off the bleed off the top of the condenser (we couldn't do this before without incurring extensive hammering) and there is no knocking at all coming from the condenser.
Thanks very much for your help.

Regards,
Greg

As Colonel Hannibal Smith always said :
"I love it when a plan comes together".

regards
katmar