Question about pressure relief valve on FT500 Hale on Deuce and a Half fire truck
The original mechanical Hale pressure relief valve with visual pressure relief activation indicator was replaced with a later model Hale control valve, but this one does not have a visual activation indicator. All seems to be working fine, but I cannot tell when the pressure relief is working. I figured that if I T into the line that goes from the pressure relief control valve to the pressure relief valve I could place a pressure switch that would illuminate a lamp if pressure is present activating the relief valve. Since this is a transfer case pto driven midship pump, engine life should be extended by controlling rpms as well as pressure and this light would assist in determining if I have enough pressure/flow at a set rpm. Also would help diagnose faulty or sticky pressure relief valves.
If my concept is correct, what psi should I expect to see in this line when activated? Any suggestions?
Any input would be appreciated.
The deuce.... an old beast? Wow... that hurts!!
Offended? Nah, just kidding... I am a believer that it is easier to keep these earlier all mechanical trucks on the road for a far longer lifetime than the cool new ones... Don't get me wrong, I appreciate the capabilities of the new ones, but my company cannot afford to either buy one or maintain one. Our main goal is to be a "first responder" to our business needs and assist the more remote locales as needed. Anyway, she sure looks good putting water out.
Thank you for clarifying many concepts that the locall FD friend and driver has spent time with us addressing. I agree with...you need to learn about friction loss in hose and nozzle flow. A 1-1/2" combination nozzle is usually around 100 gpm, and requires 100 psi of pressure for correct operation. A 200 ft line of 1-1/2" hose at 100 gpm has a friction loss of about 45 psi, so your correct pump pressure would be around 145 psi. absolute. (-14.7 psig) Operating 2 preconnects like this requires a flow of 200 gpm from the tank to the pump.
The age of this engine and the likelyhood that a 2 1/2" line was used between the tank and the pump, probably limit the flow to around 250 gpm. This arrangement will supply both 1-1/2" lines, but when you try to supply a deck gun, the flow could be considerably more that 250 gpm. A 1" tip at 50 psi flows 210 gpm; Raise the nozzle pressure to 80 psi and it flows around 270 gpm. Next std. size tip is 1 1/8 with flows of 265 and 341 gpm. respectively.
This really crystallized one of the issues...
...The amount of water that can flow from the tank to the pump is limited by the air pressure of 14.7 psi. As you approach a perfect vacuum, water will change from a liquid to a gas (water vapor), so you will never reach a pressure of zero psi. Therefore there will never be any more pressure available to get the water from the tank than that. You do not want to operate this pump under cavitation because you can destroy the pump. A creeper and a flashlight will allow you to take a look at the actual piping between the tank and the pump.[/QUOTE]
Been there... definitely the water going from the tank to the pump goes through a 2.5 in valve... having hooked up the truck to a dry hydrant I was able to build over 150-180 psi on the deck gun and have a sizeable stream... over 100+ feet through the 1" nozzle...
then something happened... a shop mechanic noticed the packing getting very hot and that it was not dripping... he loosened it some.... still no dripping... loosened it some more... Lost all Pressure.. never got it back... I can get a good prime, but cannot build pressure again... we did not run for more than 5-10 minutes... so I hope we did not screw up something major... sorry if we sound ignorant... if we do, it is because we are... I do appreciate all of your help...
any hints on adjusting a packing? Really hope we did not cook it... it costs about 200 bucks... or worse!