A Discussion on 4" LDH vs 5" LDH,

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Permalink Reply by Dave LeBlanc on March 22, 2008 at 7:34pm

Phil,

We currently use 4", the next Town north of us uses 5". The couplings are different as we have to carry adaptors for when we respond Mutual Aid.

I can't speak to the rest, except your comments about flows seem reasonable and accurate. But the crap does weigh a ton.

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Permalink Reply by Jay Michael on March 22, 2008 at 9:13pm

Phil
We use 5" never had 4" so the weight has never been an issue. Right now I can't even tell who our manufacturer is. It weighs 110# per 100' and holds about 1 gallon per foot.
We get lots of water out of the 5", we also have a good water supply. When I was an engine officer I conducted some tests with my rig. I had 300' of 5" supply from a hydrant to one piston intake and 100' to the other piston intake from a different hydrant and our 1250 gpm pump was flowing 2250 gpm. All straight stream master streams and were pito(sp) tested to determine flow.

We were looking into the hydrant assist valves (humet valve) once. I know some departments use these with 4" hose, thought they may work for us too, they don't. I laid out a hose bed (1000') let it flow through a 2" tip on a portable master stream. When doing the same thing with the assist valve at the hydrant we obtained 300 gpm less, again these were done at hydrant pressure only. Same tests were done pumping I don't have the numbers handy but still poor results.
I like 5" guys don't b**** about it.

I must ask are your supply problems caused by the 4" or water mains, Did you ever try multiple lines from the rig to the same hydrant? Usually this will help considerably. Try this, with two rigs off separate hydrants, stretch a 4" or 5" between the pumps and hook it up to the unused suction port. You should get great results. I once had 4 pumps (3-1250 &and 1-1500) hooked to three hydrants, all pumps were hooked suction to suction and was probably flowing about 9000 gpm for about 4 hours. I think the correct term for this is dual pumping, its in the IFSTA pump book. You may already be doing this, so just ignor me.
Jay

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Permalink Reply by Phil Lemire on March 23, 2008 at 10:12am

Thanks for your input Jay. Yes we have performed similar tests with our 4" hose. It is limited to carry approx 1200 gpms though. It is also limited to 180 psi pressure, so often, with long lays, it become a problem. Yes our Water supply Piping is old, in some cases over 100 yrs! Therefore we have formulated SOP's to stretch LDH to a Main St. with a larger Water Main for all 2nd alarm jobs. This creates the long lays which in turn push pump pressures up. Since the 20 psi per 100' for 4" hose is with 1000 gpm's flowing, limiting our maximum hose lay to 800-900'. For longer lays we encounter, we would either have to place a pump between this scenario, or lay double lines! With a 1500 pumper, It cannot supply it's rated capacity in this scenario through 4" hose. This is the basis for my argument to go to 5" hose.
Thanks Again,
Phil

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Permalink Reply by Chris Mc Loone on March 23, 2008 at 1:46pm

All engines in my department except for one carry 5" hose. If we lay a line for a fire, it's rarely anything but 5". My company runs two engines, each carry 1100' of 5". We have drilled using several different elevations and several different length hose lays and have foudn 5" to acommodate the flows we need. That being said, the 5" would be useless if we didn't know where to find good water. I would start with your water supply. If your supply is inadequate, making the move to 5" at this point may not be worth it. For your longer lays, consider placing pumpers in line using some sort of valve like a Humat to help move the water. Doing so should help you not reach the 180 psi in your case, or 185 psi limit of 5" hose. The friction loss with 5" is definitely lower.

Also don't forget to put your biggest pump at the hydrant.

Chris Mc Loone

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Permalink Reply by Darren Sluder on March 24, 2008 at 9:23am

My department has been using 5" for 12 years or so and have only used 5". However, according to the manufacturer training videos, 5" supplies considerable more than 4". I know this sounds silly but mathmatically, it works!
Angus Brand hose had a really good video on choices of 5" versus 3"and 4" hose.
You will need to change your truck and hydrant fittings as well as any adapters that are 4" storz. That alone is quite a cost however, the benefits out weigh the cost in my book. You might check out the angus web page to see if a video etc can assist in the friction loss analysis and fire flows.

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Permalink Reply by Don DeBias on March 26, 2008 at 4:06pm

Phil.
Are department has always used 5 inch since i joined so the weight is something i cant compare. as for volume its great i have pumped at fires with a 1000 feet of 5 inch on the ground my engine at the hydrant with a 5 and 3 inch on the hydrant to the engine and attack pumper feeding 2- 13/4 fogs and 2 1/2, engineer said he had 30 psi left on intake gauge. we run with 25 feet on front and side suction, 800 feet in rear bed. At training we ran supply engine at hydrant off that another engine and one quint, with quint flowing and 2 deck guns and numerous hand line we estamated 3000 gpm(based on tip size and pressure). one note we have good city pressure. all stortz. our dist is all the same we carry some adapters.

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