TDS 5 : Rapidrop flexible connections

Many fire sprinkler installations now make use of flexible sprinkler connections such as the Rapiddrop® system.  These types of systems normally consist of a corrugated stainless steel pipe, and a bracketing system which allows the sprinkler head to be located centrally in ceiling tile, this type of system can save a considerable amount of installation time with the 2nd fix installation pipework.

The flexible hose can be bent easily and removes the need for a number of 90° elbows.  However this flexibility comes with a cost hydraulically and therefore we must be careful when using flexible sprinkler connections that’s the hydraulic calculation represents the true situation.

The manufacturers of the flexible sprinkler connections publish detailed installation guidance which must be followed they should also provide the hydraulic equivalent length for each flexible sprinkler connection which will be different for each length they produce and for each model and manufacture.  It is important as a designer that you use the correct hydraulic length in the calculation.

To give a practical example of how you implement flexible sprinkler connections in FHC our example will use the rapid drop flexible sprinkler connection as detailed on Rapiddrop data-sheet 3.1 issue A.

The two things we need to consider when entering flexible sprinkler connection into our FHC hydraulic model is, the equivalent length of pipe and the static gain or loss due to difference in height.  The manufacturer of the flexible sprinkler connection will provide an equivalent length table such as the one below.

 

As you can see from the table above if we use a 1.22m length flexible connector the hydraulic equivalent length is 8.5 m.  So we need to input this hydraulic length into the FHC software and can do this by using the optional ‘added length’ command on the ‘ADD’ or ‘Edit’ pipe command.

We must also consider the static gain or loss for the difference in height between the fixed pipe and the position of the sprinkler at the end of the flexible connector.  If we look at the example to the left and see that the pipe is going up to the bend the top then returns back down.  As the static difference going up and returning to the same point on the pipe cancels each other out we only need to consider the difference in height between the rigid pipe and the position of the sprinkler head, in this example ‘H’ indicated the static difference in height.

We now have both pieces of information which we require, the equivalent length of the flexible sprinkler connection and the static difference in height ‘H’ we can now proceed to enter this into FHC.

For this example we going to use a Rapidrop SPB-3A flexible connection with a length of 1.54m and a drop length ‘H’ is 1 m.  To enter this information into FHC we need to draw a pipe looking down 1m in length then in the optional items ‘added length’ we can add the equivalent pipe length which in this case is 15.3 m less the 1m pipe drop which we have already entered, so we will need to enter 14.3 m

 

 

 

Now we have entered the correct data into FHC we can carried out the system calculation and we can see the results as follows:

As you can see the pipe between nodes 320 – 350 now has a total equivalent length of 16.840m this is because FHC is included the length of pipe, the additional length which we have added and the equivalent length for a tee fittings.

Pipe length =             1.00m
Flexible connection =           14.30m (15.3m less the 1m pipe drop)
Tee fitting =           1.54m
Total equv. length  =          16.84m