# Thread: Tanker Fill Appliance - Draining LDH before disconnect

1. Haven't seen any comments about size of vent - vs - fill rate. Fill rates need to be compatible with the vent or vents so that tanks are not compromised by over pressurization. I agree that when a tanker is sitting at a dump or fill site, it is not transporting water. As such the fill and dump times should be minimized. Filling at 1,000 gpm and using a 6" diameter round vent will cause about 0.96 psi when the water has to exit the vent. Doesn't seem like much, but the top of a 12' by 6' tank would see 9,976 pounds of force when it starts to overflow. Reducing the vent to 4" will result in a pressure rise to 4.34 psi. or 44,997 lbs wanting to pop the tank open. You can calculate this for your tanker by using the formula for flow from a nozzle and working backwards from a flow rate to the required nozzle pressure to cause that flow rate through your vent opening. Assuming that a particular tanker (tender) has a 10 inch round vent, then filling at 1500 gpm would cause only a 0.25 psi pressure inside the tank.
Filling this tank with 50 ft. of 5" ldh and assuming 4 feet of 4" fill pipe, a pressure of about 10 psi to overcome friction loss. You might need 20 psi or so to overcome the internal losses of the piping in the engine..so filling with LDH at not more than 40 psi engine pressure. Replacing this arrangement with 50 feet of dual 3" lines into 4 ft of 2 1/2" for fill pipe at 750 gpm per line We would need about 3 psi in the pipe and 30 psi friction loss in the hose. Allowing 20 psi for loss internal to the pump, we gat a total of 53 psi at 1500 gpm fill rate. I fail to see the advantage of struggling with 5" line when filling at rates up to 1500 gpm.
The calculations should be backed up with some tests to verify them. I have been teaching Rural F.G. Water Movement for 20 years and have yet to see an engine / tanker arrangement that can justify handling loaded LDH at a fill site. Vacuum tankers and self filling apparatus do require large suction sleeves for adequate fill rates.

2. Originally Posted by FIREMECH1
I would love to do, what you have posted. Problem is, I'm the wrench monkey.
The powers at the top, tell me what they want done, and I do it. It is rare for me to have any input on what might work better or faster.

I'm like a grain of salt in an open wound to the "gold badges". It stings them when I make a suggestion on something they spent 3 months putting to paper for something, and then have to redo it, because it works better than what they envisioned.

Their main concern is keeping the tank fill time as low as possible. I'll see if I can get what you described, and do a time run on it versus the way they want to keep doing it.

And yes, I have worked the LDH, and it wasn't fun, at all.

FM1

FM1 I feel your pain. I'm in the same boat here. The only white shirt who listens to me is the Asst Chief. Thankfully he's the Operations Officer and he backs me up 100%. The B/C's, Capts, ect..... all hate it when I come up with an idea that contradicts thiers. It's sort of a love / hate relationship. Sometimes I love it, sometimes I hate it.

Andy

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