High pressure PRVs

Replies to This Discussion

Permalink Reply by L. Chapel on December 30, 2008 at 2:40pm

We use a Akron inline pressure gauge and 60 degree elbow attached the the SPO prior to hooking the 2.5" line. See attachment.

With the inline gauge set up, the firefighter that operates the SPO will set the pressure for 'that' line once it it flowing. Just like the driver pumping at the pump panel to a discharge. You actually want more in the system than what is needed. Say the driver pumps 150 PSI to the FDC and you have 200' of attackline with a 1 1/8" smoothbore on the fire fire floor. This will require the SPO operator to give 85 PSI at the inline gauge. Because the SPO is one floor below the attackline add 5 PSI.

So over pumping is a good thing. You want a reserve; as long as you have a gauge and the capability to set the pressure at the SPO.

Look up Dave McGrail's writing on this matter. We patterned our hose pack simular to Denver FD's.

Regarding your 1.75" attacklines. We just got away from them because of the lack of flow, high friction loss and inability to have a hard hitting, far reaching stream in a commerical structure. But given your situation; make sure sure your nozzle is in the low pressure setting (55 PSI if a TFT nozzle) and at least try to get 180 GPM out of it! If you do you'll need to give 160 PSI at the SPO. 100 for friction loss, 55 for the nozzle and 5 for elevation.

Permalink Reply by Art Zern on December 30, 2008 at 2:55pm

Les,

Great response. Are you aware of anyone who makes longer 60 degree elbow with a gauge? I have been looking for the elbow with gage, so far no luck.

Again great response and good advise on Dave's writings. I would recommend Dave's book Firefighting Operations in High-rise and Standpipe Equipped Buildings.
Thanks,

Art

Permalink Reply by L. Chapel on December 30, 2008 at 3:36pm

I'm not aware of a different elbow. I know that some departments have the need to have two elbows in their kit. Then they can be twisted around to fit any need.

Art Zern said:

Les,

Great response. Are you aware of anyone who makes longer 60 degree elbow with a gauge? I have been looking for the elbow with gage, so far no luck.

Again great response and good advise on Dave's writings. I would recommend Dave's book Firefighting Operations in High-rise and Standpipe Equipped Buildings.
Thanks,

Art

Permalink Reply by Art Zern on December 30, 2008 at 4:53pm

Les,

The elbow is fine, I just can't find an elbow with the gauge in the elbow. I'm just trying to cut-down on the number of puzzle pieces.

Art

Permalink Reply by Tom Hofland on December 30, 2008 at 10:05pm

One of our challenges is that the pressure control component of the PRV is after the control valve. if you gate down the standpipe outlet with the hand wheel you do create a smaller effective orfice but the spring valve in the PRV opens to raise the discharge pressure. Its possible to gate down the max volume but almost impossible to reduce the operating pressure. One possible solution is using a hydrant gate or another appliance inline after the PRV to introduce friction and reduce pressures. This can significantly reduce flow, however, since a reduction of well over 50 PSI is "needed" for the 2.5"/SB operation.

Chief McGrails text is great and I have read it cover to cover. We have a City unique code issue (I think) which can throw a small kink in the "standard" operation.

Tom

Permalink Reply by Mike Walker on December 30, 2008 at 10:48pm

Tom

This is fantastic information; thank you so much for sharing.

So if I understand you correctly, it isn't doing any good to gate the valve down because of the spring in the PRV?

I speaking completely from a hunch but it sounds like someone is trying to get away with using a smaller handline with fog nozzles thinking that low pressure was the only problem to overcome?

I wonder what state of the art method they plan on using to stop the junk from building up in the standpipe?
Tom Hofland said:

One of our challenges is that the pressure control component of the PRV is after the control valve. if you gate down the standpipe outlet with the hand wheel you do create a smaller effective orfice but the spring valve in the PRV opens to raise the discharge pressure. Its possible to gate down the max volume but almost impossible to reduce the operating pressure. One possible solution is using a hydrant gate or another appliance inline after the PRV to introduce friction and reduce pressures. This can significantly reduce flow, however, since a reduction of well over 50 PSI is "needed" for the 2.5"/SB operation.

Chief McGrails text is great and I have read it cover to cover. We have a City unique code issue (I think) which can throw a small kink in the "standard" operation.

Tom

Permalink Reply by Tom Hofland on December 31, 2008 at 3:06pm

Mike,

We have a system which is designed around "fully sprinklered" buildings and the thought is that we can use 1.75" hose lines and fog nozzles. I know the problems with this (1 meridian plaza). That being said, its the system we have.

One possibility is using 2.5" fog nozzles (and increased staffing on the line) as a first option. Although scaling in the standpipe will eventually clog the line Im sure.

At residential high rises, however, the 1.75" hose line seems reasonable as a FIRST line. If we have enough pressure to operate a small line, why not? The fire flow requirement is well within the capacity of the 1.75" for all but the largest open floor plan luxury flats.

Wind driven fires seem like the largest challenge to my low flow (150gpm) theory. That being said the fire service isn't advancing on wind driven fires in HR buildings, even with 2.5" lines. when you watch videos and read after action reports its quite clear that accelerated initial burn rates are reducing heat release rates due to fuel reduction prior to a successful attack.

Besides, a fog pattern is an improvement to a solid stream when it comes to "pushing back" at a pressure driven fire front. Coupled with PPV (Im not one of those PPV nuts) the fog line provides the greatest probability of pushing fire out of the public hallway and protecting the rest of the building if actual entry is not possible.

This is of course NOT a solution I would advocate for commercial high rises.

Tom

Permalink Reply by Mike Walker on December 31, 2008 at 3:25pm

I have gone through the same evolution of ideas as you my brother and after years of speaking with, researching and now teaching with some very very wise people, there are some simple facts that cannot be denied.

1. My crews can only carry so much up stairs and be expected to fight fire
2. Since they are limited, they cannot be expected to carry both 1 3/4" hose and 2 1/2, it is an either or sort of thing
3. Since they can only carry one or the other, I cannot take the chance they they carry a line that is too small for the fire that will be encountered, several minutes from when they started their ascent. I can put out a small fire with a big line but I can't put out a big fire with a small line (Walker Logic)
4. Fog nozzle will, not may, will clog.

Now going back to the PRV's you mentioned; I am still perplexed as to how they cannot be adjusted. Again, I'm using Walker logic, which is sometimes flawed and is need of instruction.

I would think that no matter what the spring has to have a limit or else the valve could never be closed and since it can be closed, Walker Logic tells me that there has to be a way to open the valve partially based upon the same principle...

Please help a brother out.

Tom Hofland said:

Mike,

We have a system which is designed around "fully sprinklered" buildings and the thought is that we can use 1.75" hose lines and fog nozzles. I know the problems with this (1 meridian plaza). That being said, its the system we have.

One possibility is using 2.5" fog nozzles (and increased staffing on the line) as a first option. Although scaling in the standpipe will eventually clog the line Im sure.

At residential high rises, however, the 1.75" hose line seems reasonable as a FIRST line. If we have enough pressure to operate a small line, why not? The fire flow requirement is well within the capacity of the 1.75" for all but the largest open floor plan luxury flats.

Wind driven fires seem like the largest challenge to my low flow (150gpm) theory. That being said the fire service isn't advancing on wind driven fires in HR buildings, even with 2.5" lines. when you watch videos and read after action reports its quite clear that accelerated initial burn rates are reducing heat release rates due to fuel reduction prior to a successful attack.

Besides, a fog pattern is an improvement to a solid stream when it comes to "pushing back" at a pressure driven fire front. Coupled with PPV (Im not one of those PPV nuts) the fog line provides the greatest probability of pushing fire out of the public hallway and protecting the rest of the building if actual entry is not possible.

This is of course NOT a solution I would advocate for commercial high rises.

Tom

Permalink Reply by John Norman on January 19, 2009 at 5:27pm

Mike, the problem is not just the spring in the PRV, but also the channel through the stem that directs a flow of water from under the valve seat, up to the top portion, above the seat, which serves to balance pressures on both sides. (see attached photo) Closing the valve opening changes the pressure in this area, which allows the moveable stem to open further, letting more water through. It is similar to the spring loaded baffle in an automatic nozzle. Since the surface area of the upper diaphragm is larger than the seat of the valve the water is pushing against, the diaphragm always wins.

Attachments:

• 41727_21.JPG, 25 KB

Permalink Reply by Mike Walker on January 19, 2009 at 7:13pm

Thanks for the clarification Chief.

So it would seem like Tom would in fact need some way to gate the pressure, that is, if the PRV is set correctly.

You had mentioned in a post on another thread that FDNY sidesteps the PRV's, do you know of a way to accomplish this in the sort of building Tom described?

Permalink Reply by John Norman on January 20, 2009 at 8:12pm

I don't know of any way to sidestep the ones that are not removable or field adjustable, other than dropping down a floor or two into the top of the next lower zone if that is possible. (Usually building 30 or more stories). Going up within the same zone would work except now you are putting people above the fire without a charged line, and when the door to the fire floor is opened your hose line is in the chimney.

Mike Walker said:

Thanks for the clarification Chief.

So it would seem like Tom would in fact need some way to gate the pressure, that is, if the PRV is set correctly.

You had mentioned in a post on another thread that FDNY sidesteps the PRV's, do you know of a way to accomplish this in the sort of building Tom described?

Permalink Reply by Tom Hofland on January 20, 2009 at 11:01pm

Chief,

Considering the nature of these PRV’s what are your thoughts about making the best of them? Does a fog nozzle make sense? Or is introducing friction into the system a better option?

Is scaling or restricting volume a greater problem in your mind? I know these are not ideal trade offs but they are my reality. Another option might be the use of a smaller (high friction loss) hose to flow high volumes through a smoothbore tip? (Greater than 200 gpm through a 1.75” line and an over pressurized smoothbore tip?)

If such high flows were expected through the small line a large play pipe is probably needed to reestablish laminar flow at the discharge orifice. I am not sure how/if this would work or effect stream pattern and reach.

Tom

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