Water relays

[chris7]

Hi all,

Bringing up the subject of water relays.
In particular the fireground method of calculating distances between pumps. Only calculations I could find are from a Fire service manual 1979, giving standard relay distances on even ground.

Which as one example quotes for a required flow rate of 3500 l/min using 70mm twinned optimum distance  should be 4 lengths of hose max, at 7 bar. At 2250l/min 9 lengths of 70mm twinned.

Any updated fireground calculations ?

Chris

[Clevelandfire]

Fire service manual does give those calcs but to be honest operationally we never used them. It was a case of can appliance A feed appliance B with a satisfactory pressure Ive never known us being caught out by relays and pressures. Seems a bit adhoc but I wouldnt take much notice unless you have to pump significant height to the next appliance inline

[Nearlybaldandgrey]

I seem to remember some fireground stuff ..... max 9 lengths between base and first pump as the base pump works hardest. 10 lengths between other pumps. on undulating ground, you can add a length for every 10 metres drop and remove a length for every 10 metres rise.

The relay is of course governed by the output of the base pump.

Thank goodness for Hi-vol pumps!!

[kurnal]

Yes I recollect twin lines 70mm 2250 l/min 9-14 lengths between pumps and the variation as Baldyman says.

But these are always text book figures and in the real world you can push water much further than that. The losses due to friction, related to the velocity of the water in the pipe means that actual flow rates are critically important as losses increase exponentially related to the velocity. So if you are only actually delivering 1500l/min onto the fire, your spacing can be much greater. On the moors in the Peak we used to run single line relays very much greater distances than this to good effect provided you exercised some control at the branch end.

[Mike Buckley]

When I was on the pumps we used to carry 20 lengths of 70mm which tended to mean that the relays were 10 lengths of twinned.

However I remember working on some calculations for a pipe to be buried from an open water source to a site and the calculations showed that we would not get any water through it at all! In the end we decided that if we pumped 2000 l/m in one end we would get 2000l/m out of the other.