Cooling tower return header overpressure

[wilburfhh]

Has anyone seen some kind of overpressure protection on the cooling tower return header and/or restraint system? We had an incident in our cooling tower where the nozzle and the valve on the header separated on #4 cell (high header pressure)

Thanks

Will

 

[SNORGY]

How big is the tower?
I have seen open-ended degassing standpipes at the top of the return header risers, just high enough to provide the head required to put the water through the distribution valves feeding each cell. Difficult to overpressure a return header with that setup.


Regards,

SNORGY.

 

[KiwiMace]

Is #4 at the end of the line? Are you getting water hammer there? Given that most towers are open and vented at the hot water basin, I doubt that anything other than transient surge could have done that.

It is relatively easy to drain back a cooling tower out of operation and open up opportunities for this sort of thing on startup. Check your start up sequence for pumps starting before valves open and that kind of stuff.

 

[davefitz]

We had a total failure of a circ water return line due to a "waterhammer" event- the cause was failure of a final block valve ( butterfly) disc axis pin failure- the butterfly failed closed upon failure of the pin. Among other things , we were reminded that there is right way and wrong way to orient a butterfly valve close-coupled to an elbow.

If the waterhammer is occurring due to "normal" closure of a MOV then the final 3% closure range should be slowed down .

Another item that sometimes causes overpressure of the circ water pipe is the belated recognition that there sometimes needs to be added an add'l pressure loss at the circ water discharge to ensure the nozzle at the condenser CW outlet does not operate under vacuum- as might happen if the final circ water discharge is at a lower elevation than the condenser- this sometimes is missed in the design phase and later field modifications lead to high piping system pressures and lower circ water flows than originally intended.