foam eductor?

[osustc]

what is the maximum feet of 1 3/4 cross lay that you should use to flow foam?

[MemphisE34a]

what is the maximum feet of 1 3/4 cross lay that you should use to flow foam?

No more than 200' of 1 3/4" hose - and it doesn't matter how its loaded or where it comes from (crosslay).

Bonus question for the original poster - so how are you going to set it up if the engine has to park farther than 200' away from the incident?

(insert Jeapardy tune here)

[mdcook]

What is insert the eductor in the middle of the hose lay?
Remember the 3 P's when using a foam eductor; Pre-plan, Pressure, and Practice.
Pre-plan - Think about how far you can go from the eductor with a certain diameter of hose and still have the required amount of pressure at your nozzle. This is where Memphis34a correctly gets the 150' answer and the second P, Pressure.
Most eductors have a friction loss factor of 30% (200 psi in - 140 psi out). So if you need 100 psi at the tip, figure your friction loss of most 1 3/4" line of around 20 - 25 psi per 100' and the 140 psi from the eductor will just make the 150'. If you have hose with a lower friction loss, or larger hose, or a lower pressure nozzle, yes you can go farther and this is where the third P comes in, Practice.
Practice setting up the hose line. Get some practice foam or soap concetrate and work it out ahead of time. When you have a Class B fire on the ground is NOT the time to be thinking about what to do and this brings us full circle back to pre-plan.
Now isn't that easy

[FyredUp]

Itis really incredibly simple...no matter where you place the eductor it has to be fed 200 psi. It can be a couple of hundred feet away from the engine and as long as it gets 200 psi it will work fine. It is the inlet pressure to the eductor that is critical first and the length of hose past that secondarily. With 1 3/4 inch hose 150 feet is standard past the eductor.

I can't help myself here so here are some common foam ops problems:

1) The nozzle has to match the eductor. If it is a 125 gpm eductor the nozzle must be at least 125 gpm. If it is less gpm it will not create the proper venturi action to pull the proper amount of foam into the stream. If it is too big it may dilute the foam mixture.

2) The failure to pump the eductor at 200 psi. Anything less than that affects the venturi principle and how much foam is pulled into the stream and not be. So if you under pump it the foam mixture may be diluted and not as effective or simply not work at all.

3) Failure to maintain the eductor. After each use it needs to be flushed and made clean of all foam residue. If it isn't it will almost assuredly make the check ball stick and the eductor won't work. I always back flush, forward flush, and take the eductor apart to make sure the check ball is free and clean.

[TVFR9923]

The above posts are all good rules thumb, but for the most accurate info you need to consult your eductor's manufacturer. They all provide charts describing how long of hose lay you can use based on gpm flow, foam %, etc.

[MG3610]

Its easier to consult the manufacturers info than guess...

http://www.akronbrass.com/uploadedFi...tion-Chart.pdf

Assuming you use an educted system......

[MemphisE34a]

What is insert the eductor in the middle of the hose lay?

Yeah, but to keep friction loss down, we will extend the line with 2 1/2" hose, reduce it to a 1 1/2" fittting, hook in the eductor, and then run whatever working lengths of 1 3/4" from there.

[gunnyv]

Funny, my answer was 250', I thought WTF, then realized we have 95gpm eductors, not the 125s that limit to 150'.

Best answer is to check the manufacturer literature (like MG and TVFR said).

[Edward Hartin]

The limitation on length is based on having no more than 70% back pressure. For example, an eductor requiring 200 psi inlet pressure (typical) can have not more than 140 psi back pressure (the pressure required at the eductor outlet to overcome friction loss & head pressure and provide a nozzle pressure of 100 psi).

The length of line that you can have on the downstream side of the eductor is dependent on hose diameter and flow rate (which influence friction loss) as well as changes in elevation (influencing head pressure).

Low pressure nozzles introduce a bit of a wrinkle as many eductors were designed for use with 100 psi nozzles. Increased pressure at the nozzle will increase flow rate and may have a negative influence on foam quality.

Cheers,

[volfirie]

Always interesting this stuff! But I'll stick with the round-the-pump proportioner thanks very much. If someone else brings along carboys of concentrate we carry the hardware though. Another interesting thing? Here it's called an induction system. We can all learn, something, can't we?