Thread: What pressure?
02-20-1999, 12:10 AM #1smketrFirehouse.com Guest
What pressure is recomended for TFT? I know that it is a matter of how much water you need, but how much is too much! Some say 100 at the nozzle other say 200. I am in a small department where manpower is an issue and everybody complains that thay cann't hold the pressure. Give me recomendations or ideas on how to solve the problem.
02-20-1999, 01:34 AM #2fireFirehouse.com Guest
We too are a small department, we do 580 psi. Seems to work fine.
02-20-1999, 07:32 PM #3Ray RFirehouse.com Guest
We have used TFT Nozzles for years. Our SOP for initial attack on 150' of 1 3/4" line is 130 to 140 PSI at the pump. We then reduce pressure when doing overhaul to 60 to 80 PSi at the pump. Check the TFT website (sorry I don't have it handy). They should have some free info available on performace and pressures. They also have links to your local TFT rep who should be able to provide you with any training or guidelines you need.
02-21-1999, 11:12 AM #4NozzleFirehouse.com Guest
The pump pressure you choose is TOTALLY based on the size of the hose and what you want to flow. In the post that opened this thread there is a comment about 100 PSI at the nozzle versus 200 PSI at the nozzle. Not so!! An automatic nozzle BY DEFINITION maintains a CONSTANT pressure at the nozzle.
Think of the nozzle as a screen door with a spring. If the wind is light the screen door does not blow open. As soon as there is enough wind to overcome the force of the spring on the door it starts to move and let some of the air go around the screen. The harder the wind blows the more the door opens but the FORCE against the door is constant as set by the spring. The automatic nozzle is the same thing. It has a spring and it maintains a constant pressure if the wind blows harder (higher pump pressure) more wind goes through the door opening (around the door. If the pump pressure is INCREASED the nozzle opens up so that the increased FLOW uses more FRICTION in the hose to eat up the increased pressure. If the pump is 150 the nozzle will set itself to a flow that allows just enough water to flow to equal 50 PSI of friction loss so that 100 is left over at the nozzle. If the pump is increased to 200 the nozzle will open more (the door swings) and it will let more water flow which increases the loss in the hose to where it equals 100 PSI. 100 at the nozzle plus 100 in loss equals 200 in that case. This is one of the neatest features of automatic nozzles, if the line needs more flow all you have to do is increase the pump pressure and you will get more flow and it happens without the operator having to set dials on the nozzle all he has to do is open the bail. There is a LOT of information on this topic at the TFT web site address www.tft.com. The short answer to your question would be "Determine what flow you want to start with, figure the friction loss for the hose length that you use either by using charts or by experiment, add the pressure that you come up with to 100 PSI and that is the pump pressure"
02-23-1999, 10:42 PM #5RyWfdFirehouse.com Guest
Task Force Tip? TFT's are a dual function nozzle in which it is designed for use with 1 1/2", 1 3/4", or a 2 1/2" line. Our sop's require the pump operator to maintain 150psi nozzle pressure for the nozzle. 150? I know thats high. This is so the nozzle can operate correctly. Our sop also states that any firefighter operating the nozzle alone shall not exceed three "clicks" when opening the nozzle. This will give you about 150gpms. Each "click" on the nozzle represents 50 gpms. At any time the nozzle is operated above the three clicks, a backup firefighter is needed. This is not to say that one person can not operate this nozzle effectivly. Visit TFT's site to gain more info however as im not the expert.
02-28-1999, 10:39 AM #6NozzleFirehouse.com Guest
I really think that the 150 that your department SOP has you maintain is the pump pressure not the nozzle pressure. There is pressure loss in the hose line when it is flowing water. The clicks do NOT equate to a particular flow. We designed them to be as proportional as possible but they do not equal 50 GPM per click. If for example the pump pressure was at 120 then even with the nozzle full open the flow would only be about 100 GPM so in that case when the nozzle was open the first two clicks the valve would have enough flow area such that further opening would have no affect on the flow. The reason that one nozzle can be used on so many different hose lines is that the nozzle has a very wide FLOW range from 50 to 350 GPM so it is properly sized for whatever size handline it is attached too.
02-28-1999, 10:20 PM #7RyWfdFirehouse.com Guest
Nozzle I stand corrected.... that is the pump pressure not the nozzle pressure. and thanks for the information.
03-02-1999, 11:07 PM #8cmillerFirehouse.com Guest
We run with 1 3/4" TFT nozzles 200' preconnected at 150 lbs at the pump panel to get 100 lbs at the nozzle. As per our SOPs there is always 2 men on an 1 3/4" line. The problem with automatic nozzles is that the stream always looks the same no matter the pressure. You must rely on the operator to give you enough pressure to obtain the correct GPM for the fire load.
03-03-1999, 05:00 PM #9kaFirehouse.com Guest
<<The problem with automatic nozzles is that the stream always looks the same no matter the pressure.>>
Huh? That isn't even true if you only use nozzles right out of the box. You can look at any automatic stream and determine pretty close what the actual flow is. There is a big difference between 50 and 350, 100 and 150, 150 and 200 etc. The stream reach isn't there the stream is not as full the nozzle doesn't sing the same.
Plus the most important thing you left out is machines are not holding these things, living breathing firefighters are. The automatics have this really cool top secret star wars thing built into them that tells you approxamately what they are flowing all the time that doesn't use batteries, computers, wires, gears, motors, or any moving part and it always works, plus it has another feature to let you know it is flowing too much water for the crew on the line.
Everytime you open the nozzle no matter what the flow is, it is called nozzle reaction. If the fire fighter cannot discern between 50 and 200 gpm then maybe it is time to start training. I've got firefighters from rookie to chief who can tell by feel, look and sound.
If you land on your butt you just found the automatic feature that says your not holding it right or you need to learn to open shutoffs slower. If it makes you back up you're probably not holding it right and have attained your individual low limit standing, neel and you can handle it. These two options are no cost options offered by all manufacturers and universally understood by all.
<<<You must rely on the operator to give you enough pressure to obtain the correct GPM for the fire load.>>>
AND that isn't the case with every other nozzle on earth? YOu left out the part about the nozzle offering forgiveness that smoothbores don't offer and it always out reaches them.
That is exactly not the concept that brought automatics to the fire service. The idea was one pump pressure all the time and let the guy at the nozzle determine how much was needed by opening the shutoff to the point of need or staffing. Pump a 1 1/2(one and one half) inch line at 250 psi and you'll flow 200 gpm through a 150 foot line everytime. We happen to use a booster reel for flows that low.
If only one firefighter is on the line and cannot open the line all the way standing they can neel down and leter rip. Lean against a wall, hook the pistol grip over the wall or use a 10 foot length of 2 1/2" hose on the end to eat 95% of the 100 pound reaction.
Why let the pump operator control the flow, work it out at the station and always pump the max. Let the nozzle guy determine what he needs and if things go to beans it is there ready to use.
Leave the fire flow and hydraulics back at the station. All attack lines have approxamately 3 times there gpm flow in fire kiling capability measured in square feet, so the guy with the booster reel flowing 180 gpm can handle almost 600 square feet of fire. The guy with the 1 1/8 smooth bore on the 2 1/2" and a crew four times larger can handle 750 square feet. The guy with a 1 3/4" inch line and automatic with a PDP of 250 can take on 760 square feet of fire a 2 inch line 1060 square feet and the 1 1/2" 600 sq ft. At somepoint 30 to 60 seconds into the application if that doesn't do it you might want to be standing outside.
03-03-1999, 08:23 PM #10Water ManFirehouse.com Guest
Before this digresses into an I LOVE or I HATE Smooth bore nozzles, lets stay with the subject of the indication to the firefighter of what they are flowing and the impression that because a stream looks good, that it is somehow deceiving the firefighters as to what they are flowing. KA's comments are for the most part right on as regards the best indicator to the crew as to what they are flowing...(disregarding what for some would be extremes. For example the 250 psi for most is not a comfortableor practical pressure at the pump. )
It is precisely because an automatic nozzle is maintaining the pressure constant (AT THE NOZZLE) that allows a great simplification of the standard reaction formula. That is:
Nozzle reaction = .0505 times the sq.root of the nozzle Pressure. Assuming the nozzle is a 100 psi constant pressure nozzle, this is now simplified to .5 ( or 1/2) the GPM equals the nozzle reaction in pounds of force. Imagine then, being "IN IT"... number 1 it is Highly likely you can't see that really nice stream anyway due to the smoke and/or darkness. However, crawling in you open the line up. The ONLY true indicator you have is the reaction in your hands... Can you tell the difference between 50 lbs reaction (100 GPM) and 100 lbs reaction (200 GPM) ? It's quite easy.
The very important difference is that the reaction on an automatic nozzle is PROPORTIONAL to the FLOW. If you increase FLOW 10%, you will increase the reaction 10% and visa versa... this is not the case with a nozzle with a fixed orifice size (yes this includes fixed gallonage combination nozzles, selectable nozzles, and also the smooth bores)....
Example: a Fixed 95 GPM. (or for simplicity, call it a 100 GPM nozzle). To increase the flow 20 % ( to 120 GPM) through that nozzle and that fixed opening would require a nozzle pressure of 145 to 150 psi. and the reaction using the above formula would be 74 lbs...
The automatic, because the nozzle pressure remains constant, would increase to 60 lbs.
The automatic? 1/2 x 120 GPM, or 50 lbs original reaction increased the flow of 20%, either way it still comes out to 60 lbs reaction....
With the fixed opening for the 20% flow increase, you are getting a 48% REACTION increase. Assuming you can't see the stream, which would be the most misleading, as to which was delivering more flow...?
This happens the other direction as well (as in a 20% DECREASE in flow results in a 48% DECREASE in reaction) With a fixed opening, the reaction is varying as the SQUARE of the nozzle pressure. It is NEVER proportional to the flow.
Because we eliminate the nozzle pressure variable and make it a constant, the reaction then becomes a much better indicator to those on the line as to what they are flowing...
An alternativc to consider:
If you are looking to reduce the reaction on the line, most all manufacturers have a lowered pressure version of the same automatic nozzles which would give you a reduced reaction for a given flow. The flow change as it relates to reaction change would still be proportional. It would be a smaller constant TIMES the GPM. For instance an automatic operating at 70 psi constant pressure would have a nozzle reaction of .42 x(GPM) Other nozzles are available as well which are switchable between a high (100 psi) and a lower (70-75psi) pressure setting to adapt to a given current situation. Note however, that for LIKE flows, reducing the pressure from 100 to 70 is only going to reduce the actual reaction by about 13%..
You wont get "something for nothing" here.... By using only a low pressure nozzle, the other advantages of the higher pressure will be compromised, such as the density of the fog pattern, and some effect on stream reach, and impact force (punch and action of the stream).
Each Department has to evaluate their own operations, manning, response, and capabilities to determine which nozzle alternative works best for them. Those that will be happiest with their decision will be those that do their homework in advance of the 'new' nozzles showing up on the doorstep.
[This message has been edited by Water Man (edited March 03, 1999).]
03-04-1999, 01:31 AM #11kaFirehouse.com Guest
<<<...(disregarding what for some would be extremes. For example the 250 psi for most is not a comfortable or practical pressure at the pump. )>>>
Why? Explain comfortable and practical please.
If 200 psi was ok with 300 psi test hose of the 70's and 80's and we use 500 psi working and 1500 psi test hose on a 600 psi tested pump today?
It used to be a 1.5 to 1 safety factor now a 6 to 1.
Engine rpm's of the 70's and 80's would be in the 2300 to 3800 rpm range versus today's peaceful 1300 to 1700. In fact less than 200 rpm difference between 150 psi and 250 gpm.
The higher EP allows a smaller lighter weight attack line which saves the crews back but still maintains high flow.
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