Friction loss for Flanged Concentric reducer

[SPKR]

I have been searching for an equivalent length of a 5" by 6" concentric reducer that can be used for my fire sprinkler calculation. I cant seem to find anything. NFPA 13 does not list an equivalent length for reducers, but I have a reviewer that is asking for it. Anyone have a source for that, or a very simple formula that can be shared ?

 

[TenPenny]

Here is one source, scroll down a bit, and read the commentary.

Equivalent length of pipe fittings for plastic and steel pipe

Table of equivalent lengths of pipe fittings and valves in plastic (PVC, CPVC, HDPE, GRP/FRP) and steel pipes

www.katmarsoftware.com

3. Equivalent Length Values for Reducers (Turbulent Flow Only)​

The pressure drop across a reducer is not often modeled using the Equivalent Length Method because reducers have 2 characteristic diameters. Also, the Equivalent Lengths for reducers are not as constant across changes in size and Reynolds Numbers as they are for the fittings listed in section 2 above. And of course the pressure drop through a reducer is different when the flow is from the large end to the small than it is with reverse flow.

Nevertheless, reducers are commonly used fittings and it is necessary to be able to model their pressure losses to some degree if we are going to use the Equivalent Length Method at all. We can do this if we use the ratio of the downstream diameter to the upstream diameter to specify a reducer as a particular fitting with its own Equivalent Length. Although the fittings in Section 2 above each had only one Equivalent Length we will have to accept that reducers will have 2 Equivalent Lengths - one for each flow direction.

The Equivalent Lengths in the Tables below can be expected to give accuracies of 50% or better. While this may sound extremely poor, it does at least give an indication of whether the pressure drop across the reducer is a significant portion of the overall pressure drop. This will give the engineer a basis on which to decide whether or not further work is justified or required to be able to come to a sufficiently accurate result. If better accuracy is required the more sophisticated methods as implemented in AioFlo should be considered. The Equivalent Length Method for reducers can only be used for turbulent flow (Reynolds Number > 4000).

Steel pipe reducers are made with well rounded transitions between the straight and tapered portions. This significantly decreases the pressure drop when the reducer is used in the converging mode - i.e. with flow from the larger diameter towards the smaller diameter. Commonly available plastic reducers are not made this way. Plastic reducers generally have sharp corners between the straight and tapered portions, and the tapers are usually very steep. The Equivalent Lengths given below for plastic reducers are based on a sudden contraction. This may be a bit conservative, but in the absence of better data this gives a "safe" estimate. Equivalent Lengths are also given for sudden contractions in steel pipe and for smoothly rounded steel pipe reducers. The Equivalent Lengths in the Table below are based on the upstream diameter of the reducers.

Note that the pressure losses that are modeled with this method are only those due to the friction and form losses in the fitting and do not include any consideration of the changes in pressure brought about by the net change in velocity. The change in pressure with a change in velocity is described by the Bernoulli Equation and is a completely different effect from what is being considered here, although of course the Bernoulli Effect has to be taken into account in the overall design of the pipeline. This is discussed in more detail in another article and is illustrated in this AioFlo Example Calculation.

Do/Di (Note 1)​	Plastic Sudden Contraction​	Steel Sudden Contraction​	Steel Pipe Reducer​
0.9​	10​	9​	3​
0.8​	30​	27​	8​
0.7​	75​	65​	18​
0.6​	175​	150​	38​
0.5​	420​	370​	85​
0.4​	1150​	1000​	220​

Table of Equivalent Lengths (Le/D) for Reducers in Converging Mode
Based on Upstream Diameter and Turbulent Flow

( Note 1 : Do/Di = downstream diameter / upstream diameter )