I've got a quick question for you guys. I'm on a smaller volunteer dept, I'm one of the younger guys, and though I'm off my probation, I'm still the rookie of course. Anyway, on to the question.
At a drill the other night we were doing the NFPA engine evolution 1 - forward lay from hydrant, pull two attack lines and flow water, pretty simple stuff. Due to space constrains we only had 50ft of 3" supply line from the hydrant to the engine. I was on the pump, and I'm certainly no pump expert or anything, but we make sure everybody can at least get water flowing if need be. Anyway, I'm pumping along, when one of our guys decides he would like to pull another line and asked me if we could. I saw I was running 50psi residual pressure so I said go ahead. However, one of our older guys standing nearby told me to be very careful not to let the residual pressure drop too much or you would collapse the water main. I said you didn't have to worry about collapsing the main because first you would simply collapse the supply line. His reply was "with the old mains in this part of town you have to be real careful". He also said you never want to pull a vacuum on a hydrant - I though you could only pull vacuum on a hydrant if you were using hard suction. I let the issue drop since he was my senior, but I've been wondering about this since.
I always try to stay over 20psi residual when I'm on the pump, but I'd always thought that as you start getting below that you would collapse your hose and didn't have to worry about the mains. So the question is - is it possible to collapse mains in a scenerio like this?
At a drill the other night we were doing the NFPA engine evolution 1 - forward lay from hydrant, pull two attack lines and flow water, pretty simple stuff. Due to space constrains we only had 50ft of 3" supply line from the hydrant to the engine. I was on the pump, and I'm certainly no pump expert or anything, but we make sure everybody can at least get water flowing if need be. Anyway, I'm pumping along, when one of our guys decides he would like to pull another line and asked me if we could. I saw I was running 50psi residual pressure so I said go ahead. However, one of our older guys standing nearby told me to be very careful not to let the residual pressure drop too much or you would collapse the water main. I said you didn't have to worry about collapsing the main because first you would simply collapse the supply line. His reply was "with the old mains in this part of town you have to be real careful". He also said you never want to pull a vacuum on a hydrant - I though you could only pull vacuum on a hydrant if you were using hard suction. I let the issue drop since he was my senior, but I've been wondering about this since.
I always try to stay over 20psi residual when I'm on the pump, but I'd always thought that as you start getting below that you would collapse your hose and didn't have to worry about the mains. So the question is - is it possible to collapse mains in a scenerio like this?
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