Using the Pierce engines that I am familiar with, if I am the second truck, and you have started a fire attack with your first in engine, I can pump from my 5" outlet on the pump pannel into the 5" intake on the right side of the engine. Then, it is easier for the second engine to take on water & continuiously feed the first engine. If you bypass the tank & use the water from the second truck, when that truck has to draft from the dump tank which hopefully will be filled by this time, you will have a full tank of water to use while I am taking on more water OR drafting straight from the tank to feed your truck.
This is why we have to calculate fire flows. I have an engine with 1500 gal of water so @ 125gpm, I have about 12 minutes of attack time. If I'm lucky, I'm going to get the 2000gal tanker and I now have another 16 mins. So @ 125 gpm, I am going to have about 28 mins of water. On many fires 3500 gal will be enough to do the job, we get the fire knocked down in say 8-10 minutes if everything goes right & still have water left over :) we hope. Then again, 3500 gal can be a drop in a bucket depending on the nature of the fire. We need to do some quick calculations when we get there to find out if we have enough resources.
Can I ask why you have a modern engine with 1500 gallons of water, probably a 1250 pump, I bet you have even have modern 1.75" attack lines... but you have old school 1.5" nozzles flowing 125 gpm???
As Dave said, this can go pretty deep. Do you understand that my nozzles flow 50gpm more water with about 50 lbs of less nozzle reaction and LESS MUSCLE useage, if you flow yours correctly. Today's interior attack fire needs 180 per line and your 125 nozzles were designed for 1.5" hose. Therefore they should be placed on a trashline for dumpster fires or placed on a shelf to use for a hydraulics training class.
125 nozzles on a 200' 1.75" handline has about 80-85 pounds of NR. Therefore most fire officers and firefighters who have to fight the pressures ask for the PSI to be reduced by a few pounds, but what you are doing is robbing the end user, the brother or sister on the knob of valuable GPM and hence we have people going to work with 80-90 gpm with what they think is a 125 attack line. Now you are looking at being behind 80+ gpm in the firefight compared to new modern nozzles.
You have to pull two attack lines to flow what my TWO firefighters are flowing comfortably with ONE line. If I pull two lines (attack and back-up) done at every fire, you need to pull two fire attack lines and one for backup = (3).
Now lets look at pump pressures and wear/tear on your equipment and personnel. Your nozzles are designed for 100 psi at the tip. What is your hydraulics calculation to flow a 125/100/#80NR nozzle with a 200' attack line? My D.O is flowing only 134 psi to have a nice and comfortable 175 GPM come out of the other end, my pump is almost idling... now what is your pump pressure?
So flowing GPM for GPM with the two different set-ups, how many minutes you have now??? Not to mention the inadequate and deadly reduction in fireflow which has been a direct result to firefighters being overrun by fire and flashover.
I suppose that we consistantly practice drafting, even though all around me is fully hydranted, is that we provide trucks and crews all summer for long distance Strike Teams. Very few hydrants out in the bush!
Hay Dave our engine has a valve right next to the pump on the 6" draft intake which allows us to pre prime the draft intake while we are doing initial attack from the truck tank. We can then open the valve and switch to draft without having to shut down.The key to this is to open the valve for draft before the onboard water is gone. This allows the pump to continually move water from the onboard tank and work out the little bit of air between the pump and valve until full draft is picked up. If we pump the onboard tank dry before the draft is started then we do have to shut down to prime the pump from draft.
God Bless You LT Lake. That is what I was waiting to hear. You how ever do it a little bit different than we do. We have the same valving on our intakes. We slowing open the valve while we are pumping. By doing so we expel the air back Thur the tank fill valve that we have half open. Which you should have half open anyway. We accomplish the same thing. That is start a draft without shutting down pump operation.
Glad I could help Dave. I guess I'm not sure if the air ends up in the tank or down the hand line but now that you bring it up the tank fill valve is open as well as the tank to pump valve. We have auto valves rather than manual so they are either open or closed.
We cover over 100 sq miles and only about 2 sq miles of that has plugs. We do alot of drafting. We also have several dry hydrants in the district also. Those make it really nice for drafting from a static source.
Yes your air goes to the tank with the tank fill valve. Think of this way. Your air is going to take the route of least resistant. You have 3" tank fill valve. You have a 1.75 or 1.50 hand line open. The pressure you have going to the hand lines will route your air Thur the tank fill valve because you do not have the resistant that is at the hand line