Quick Connects Dangerous?

[ClayFire65]

There is a difference of opinion at the fire department I'm on. We have a water tanker equipped with two 3" quick connect inlets at the rear of the truck. When doing tanker shuttles or just filling the tanker, we have 2 short sections of 3" hose we connect to the inlets with quick connect couplings. At the other end of the hose lines we have gate valves to hook up to the hydrant. Now here's where the diff. of opinion is. When the tanker is full, or close to being full, which do you close first? The gate valve at the hydrant, or the tank fill valve on the truck? Some firemen on my dept say it doesn't matter, you can close them in either order. But some firemen say you should close the gate valve at the hydrant first to avoid the risk of having the quick connect coupling burst. This burst being due to the pressure dead-heading at the truck's inlet. So what is your opinion and why? Thanks for your response.
-Mike Szucs, FF/EMT

[IJHumberson]

If you are flowing two 3" lines from one hydrant, it would seem to me that, unless you are on a dead-end line, or a poor supply area, the pressure at the fitting would not be that much greater with the valve closed than it would with the valve open, so I wouldn't see a problem with closing the valves at the tanker first, if so desired. Besides, those fittings are designed to handle the same pressures as the hose, the valves and all the other components, so why would they be more likely to fail quicker than the other components? The only time that I have seen quick-connect fittings come apart is when they weren't fully engaged and locked into position.

I say it doesn't matter which valve is closed first, but if you close the valves at the tanker first, be sure to do it sloooooooowly so as to not create a water hammer that could rupture the hose or even the street main.

That's just my opion - an you know what they say about opinions...

[ME93]

It really shouldn't matter which is turned off first.

The pressure in the hose should not effect it at all. If it does I would say you should have replaced it anyway.

[Indiana]

We use the same setup. I suggest shut the gate at the hydrant first.
1.It will relieve the pressure on the fitting and make it easier to disconnect. Instead of hydrant pressure on the coupling, trapped when you close the tank valve.(60 or 80 psi or more?) You only have the head pressure of the tank.(.5 psi per foot of tank height)
2.If the tank valves are 1/4 turn and the hydrant valves are gates. Less chance of a burst main.

If you do close the tank first, open it again after shutting the hydrant to relieve the pressure before you disconnect. If the hydrant has much pressure the couplers can pop off with quite a bit of force.
You did'nt say if your couplers are stainless, aluminum, or plastic. Don't think I'd trust plastic under much pressure.

[jsdobson]

If failure of the coupling is a concern, are you securing the end of the supply line with rope or webbing to prevent a "wild hose" from whipping uncontrollably ?

[bobsnyder]

There are a few issues here, so I'll just take them in the order they occur to me:

1. When you say "quick connect inlets," are you talking about Storz couplings or are you talking about the older-style snap-on couplings, most commonly seen on older portable pumps? If you're talking about Storz couplings, I'd find it very hard to believe that you have hydrant pressure capable of making your couplings fail, as long as you properly test and maintain your hose and you keep it free of twists when you're using it in the field. Snap-ons are more risky, and I just wouldn't use them at all.

2. If your tank fills are direct (don't go through a pump), then you will have a significant pressure difference in the fill hose between the times when you're flowing water and the times that you'd be sitting there with the tanker's valves closed and hydrant open. Essentially, this is because direct fills provide very little resistance to the flowing water, while the closed valve provides maximum resistance. For proof, fill a tanker from a static source using a drafting engine. You'll see that, no matter how much you crank up the RPMs on the engine, building pressure in your discharge line will be nearly impossible as long as the valves on the tanker are open and you're flowing direct to the tank. Then, see what happens as you SLOWLY BEGIN to close the valves on the tanker (don't ram them closed, or you'll risk pump damage). You'll see pressure climb as the closing valve provides increasing resistance. This, however, isn't the best reason to close the hydrant first.

3. FO2's reasons for shutting the hydrant first are much better reasons than the fear of burst hose or couplings, assuming again that your hose is properly maintained and is the proper hose for the job.

Hope this helps.

[fireeater650]

Clayfire-

Our tanker's fill system is set up identically to yours, matter of fact when I was reading it I thought it was someone from my dept. I like to shut down the hydrant first because it keeps me from getting wet. if you shut the fill valve first the pressure from the the hydrant will find the little pin holes and give you a good squirt if you aren't careful.

[lang]

Allow me to put my 2 cents into the bucket.

I'm a fire fighter at a petrochemical refinery where we work with normal hydrant pressure of 13 bar (188 psi). If needed it can be boosted to 16 bar (232 psi). All our small diameter hose are fitted with instataneous (quick connect) couplings while the large diameter hose are fitted with storz couplings. For the past 12 years I can not recall a single incident where either failed due to the pressure. As for the question on which of the valves to close I will suggest that you close your hydrant first to prevent pressure build-up in your hose which can make it difficult and dangerous to uncouple.

Regards

[ 12-12-2001: Message edited by: lang ]