CAFS question

Replies to This Discussion

Permalink Reply by Jeff Cotner on April 15, 2008 at 3:39pm

Hello, The story about the 5 inch hose has no merit. The CAFS is made on the discharge side of the pump. This has nothing to do with how big the line is feeding the truck. With that being said, what does make a difference is the intake pressure. With CAFS operation being operated around 80-90psi, if you have an intake pressure of 100psi, it can cause you problems. What most people are doing with the intake lines are using them on a direct tank fill. This makes things much easier for the pump operator if they are working from the tank and just fill the tank as needed from the intake water source whatever that may be.

Permalink Reply by scott corrigan on October 21, 2008 at 1:33am

This is what we faced with the purchase of 3 CAFS pumpers. We found that in our more densely populated downtown sector we have very high PSI hydrants. We were having our governors dump on us. We retro fitted one of our units with a direct tank fill w 1/2" line that ran off the LDH intake, it is an either or. The downside is you are limited by the size of the line running from your tank to pump. Usually restricts your avaialbe flow to around 500 gpm sustanied before cavitation. If we begin offensive with CAFS and need to transition to larger lines with more GPM than the direct tank fill can accodmodate then we open up the LDH intake.

I am very interested to hear what your GPM flows are for interior attack lines? 1 3/4" and 2 1/2"

Enjoy

Permalink Reply by Alan Butsch on January 25, 2009 at 7:56pm

Our engines use a auto tank fill off an intake as well. The fill piping is 3" to a 2.5" valve. Yesterday it filled a 750 gpm booster tank in about a minute off of a 60 psi hydrant - so as with anything it depends on what you spec. We plan to use a similar strategy as mentioned above - 500 gpm (three line) fire = CAFS; big fire = big water, no CAFS and open up the intake.

Permalink Reply by Nick Perkins on March 30, 2009 at 2:27pm

Your intake PRESSURE can cause a problem if you are running a pierce. The manufacturer recommends a difference of 50PSI for your intake VS discharge pressure. This allows for "proper cooling" of the compressor. Most of our drivers( including myself when I drove) don't follow this. BUT we have also shredded about a dozen compressors over the past 14 years. The easy fix is to pump from the tank. We have also had problems since our new apparatus don't have true discharge relief valves, just pressure governors, this can lead to some problems like Jeff mentioned of lines having to much pressure on a CAFS line since the governor can only drop the pump to idle and not dump water. On my shift we had to train our newer and older drivers on how to control intake pressures like adjusting the trucks intake pressure relief valve etc.

PS we run CAFS (since 1996) on all class A fires and I am still alive. But I may be just lucky.

Permalink Reply by Michael J. Anderson on April 3, 2009 at 9:55am

Clyde,

Which manufacturer is your unit made by? I have heard this same situation from one of our surrounding area departments. What is has to do with their system is the CAFS inductor. It has pressure differential requirements that are similar to a in-line foam eductor. The differentials fall into line with the cooling of the compressor unit. Their unit cannot be supplied by a 5 inch line unless they are flowing large amounts of water. They must use 3 inch supply line for "bread and butter" residential fires.

I do not thik it is from turbulence.

Permalink Reply by Clyde Beaver on April 4, 2009 at 5:56pm

Michael,

The rig that I am talking about does not belong to my department, however it was built by KME. My department is specing a new rig now and unfortunately it will not have a CAFS system but it will have an injected system, probably a Foam Pro 2002 or similar. The main reason we wont have CAFS is cost.

Permalink Reply by Jeff Cotner on April 7, 2009 at 10:07am

I agree with everything you are saying. There are still a lot of sales people selling fire engines that don't get it. Every CAFS engine should have a direct tank fill so we are not fighting these high water pressures. It makes the pump operators job much easier.

Michael J. Anderson said:

Clyde,

Which manufacturer is your unit made by? I have heard this same situation from one of our surrounding area departments. What is has to do with their system is the CAFS inductor. It has pressure differential requirements that are similar to a in-line foam eductor. The differentials fall into line with the cooling of the compressor unit. Their unit cannot be supplied by a 5 inch line unless they are flowing large amounts of water. They must use 3 inch supply line for "bread and butter" residential fires.

I do not thik it is from turbulence.

Permalink Reply by Mark Cummins on July 15, 2009 at 11:44am

The problem is the manufacturers don't get it.
They need to sell big water pumps, CAFS doesn't need big water to extinguish BIG fires. (If you know how to use CAFS).
CAFS does not require ballanced pressure, run your pumps at any pressure you want and regulate the VOLUME with your panel valve. You need the RPM to get the compressor revs but that cause the BIG WATER pumps to heat up. Bad engineering. Some fire departments just can't give up big water and trust the years of CAFS proof. The manufacturers aren't going to give up big pumps.

The answer might be provide a private fire service that gets and uses the best designed CAFS equipment that gives all the advantages of true CAFS applications. (NO! I do not any longer manufacture CAFS). But I do still use them.

The Aerial CAFS is one of the best configurations I've ever used. But don't retrofit a compressor on your truck, bring the compressor to the fire scene and pump water at 100 psi from any of your engines to the manifold on the compressor, control the water volume downstream of the check valve on the compressor manifold. You don't need more than 50 gpm of water to get a good CAFS attack volume and area coverage of more than 1,000 gpm of foam. I know a lot of you can't believe this, but this is the way CAFS works. It's not the water, it's the bubbles that do the work.

Permalink Reply by Zachary E. Smith on January 27, 2010 at 8:54pm

Having dealt with this as an engineer, its the PTO driven air compressor that is the real culprit. When you flow high pressure, and/or any water into the pump, it doesnt require the RPM's from the transmission to maintain your pressure. However, your compressor requires the High RPMs to generate enough CFM's of air to get the bubbles you need to make a great CAFs stream. Pump manufacturers recommend gating pump intakes, or usually a direct tank fill linked to the water gauge to regulate flow of water into the system. Hale and Waterous are like this. I dont have much experience with the Husky system.

Permalink Reply by mike on December 16, 2010 at 4:10pm

hi there.  My dept. is just looking into cafs.  Could someone explain exactly why it is bad to run cafs thru a hydrant supply line versus a dedicated fill valve?  Is it aggitation, lack of cooling or just pressures wanting to level out?  I just don't totally understand why you can't just cut back your intake valve to a desirable pressure level rather than run it thru a tank fill.  Thanks.

 

 

Permalink Reply by Alan Butsch on February 5, 2011 at 4:05pm

Mike,

 

  It depends on the manufacturer.  Pierce's Husky does require a pressure gradient for cooling.  The Hale does not - but does require high RPMs on pump shaft to drive the compressor.  You could regulate incoming volume and psi with an intake valve - if you have one - or by "overdriving" an internal relief valve such as the TPM system from Hale.  However this requires continual adjustment by the PO.  Running it through a fill valve and the tank is much simpler.  

 

Thanks

Alan Butsch

alan.butsch@montgomerycountymd.gov

Permalink Reply by Travis Coates on February 10, 2011 at 11:08am

New to CAFS and was wondering what was meant by needing a "pressure gradient for cooling"  Thanks.  Travis.

Alan Butsch said:

Mike,

 

  It depends on the manufacturer.  Pierce's Husky does require a pressure gradient for cooling.  The Hale does not - but does require high RPMs on pump shaft to drive the compressor.  You could regulate incoming volume and psi with an intake valve - if you have one - or by "overdriving" an internal relief valve such as the TPM system from Hale.  However this requires continual adjustment by the PO.  Running it through a fill valve and the tank is much simpler.  

 

Thanks

Alan Butsch

alan.butsch@montgomerycountymd.gov

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