Turn it Up! Putting the 100 PSI Pump Pressure Myth to the Test

For many years, as I have taken pump courses, participated in training sessions and taught pump programs I come across a disturbing phenomenon with regard to what pressures pump operators are using when flowing to their handlines.  Many times in the discussions, someone throws out there that they pump the preconnects at 100 PSI and allow the nozzleman to choose to have the pressure increased or decreased upon request.  This "works" for alot of departments, but it doesn't really work well if you consider that an attack hoseline system should be something designed and implemented with alot of different considerations made.  Some of these considerations should include your desired hose diameter, length, type of nozzle, typical staffing, desired maximum nozzle flow and backpressure and more.  It is a decision making process given little to no attention in many fire departments which often results in a terrible mismatch of hose and nozzles and firefighters who struggle to use the end result either because the inadequate water flow cannot extinguish the fire or because they cannot handle the backpressure off the fire stream.

I have been lucky to participate in many good discussions, review alot of good data and obtain alot of my own data about hose and nozzle selection in the past few years.  As I am writing this, I have to admit that 5 years ago, I feel like I knew not even half of what I know now, and I still feel like there's much to learn to evaluate and implement a good combination of hose and nozzles for a functional and effective attack hoseline system.

In this article I want to address the specific issue of under pumping attack lines.  Preconnected attack lines in particular.  There isn't any solid data, nor is there a way to gather it, but I feel pretty confident that many engine companies are under performing in GPM delivery because they haven't put the pieces of the system together and/or done the tests to determine the proper flow of their attack hose/nozzle systems.

The end goal of our tests is a 150 GPM fire stream.  The relative comparisons are meant to see how close we can get to the starting benchmark of 150 GPM with improper and then proper PDP.  I consider the 100 PSI PDP test results failing if they do not meet 150 GPM, and there should be no surprise that they didn't.

I want to make it very clear that the goal here is not to discredit the nozzles.  Each nozzle worked exactly as designed, when it was used properly and pumped properly.  This article is a comparison of three different nozzles being improperly utilized, on purpose, to illustrate the impact it has on total water flow delivery.  I have my preference in nozzles, but that isn't relevant to this piece of work.

Earlier this week I gathered several nozzles to evaluate how they would perform when pumped at the 100 PSI pump discharge pressure (PDP). The three nozzles evaluated were the 50-350 GPM Automatic Task Force Tip, 7/8" smoothbore tip and SM-30 Elkhart Automatic.  With the help of several firefighters we set up a series of tests, while we also conducted testing for our preconnected attack lines.

The test setup was 200 feet of rubber lined double jacket 1 3/4" fire hose.  Test gauge was installed at the front bumper connection, and at the inlet of the nozzle.  There was no elevation and no other influencing factors.  I chose 200', as it represents a very typical length preconnected attack hoseline.  Its important to note that different brands of hose will vary in internal diameter, and different lengths of hose will yield different results.  There are many variables which make the collection of data for your individual department important.  The results we have represent fairly accurate numbers, but I like to say that its not perfect.  The relative differences between each PDP for the given nozzle are the most important part of this comparison.

The hose we used has a known internal diameter of 1.81" per the manufacturer.  The hose was connected to the front bumper discharge of the rig, which is a typical connection for our fire department operations and represents what I feel is a realistic amount of plumbing loss.  When utilizing a crosslay with swivel, it is typical to have at least two 90 degree bends in the piping.  The rig used was found to have approx 10-15 PSI of loss in the piping to this discharge at 150 GPM.

The three nozzles tested were the second third and fourth from the left

Once the hose was laid out and the gauges installed, the testing commenced.  The rig was connected to a hydrant via 25' front soft sleeve.  The hydrant pressure and flow were greater than necessary for the low volume testing.  Initial flows were gated  at the discharge valve to achieve 100 PSI.  Proper pump pressures required increasing the RPM via the electronic governor to obtain the desired PDP.

The test nozzles had a 1 1/2" inline gauge installed at the inlet with a 0-300 PSI gauge

Nozzle readings were obtained at the inlet gauge, with the understanding that this represents a slight inaccuracy.

The line was operated from a discharge which is manifolded through a Hale foam system, with a paddlewheel flow sensor.  The flow sensor was checked and found to be fairly close to accurate by use of a pitot tube.

Test 1.
The testing began with the TFT automatic nozzle.  As I mentioned, the goal was to pump the lines at 100 PSI at the discharge gauge and see what the yield GPM was.  When evaluating the TFT, little nozzle reaction was noted, however we did not measure reaction force.  One firefighter was able to handle the hose easily.  The stream shows the focus point of the water fairly close to the baffle, which is a good visual indicator of low flow.  We "trimmed" the stream back a bit from the stop point where it would be as close to a solid column of water as possible without the water colliding and crossing over itself.  Anyone who works with automatics knows that you have to tweak the nozzle pattern adjustment as the flow increases and decreases to keep the straight stream ideal, since the movement of the baffle changes the pattern slightly.

A flow of 85 GPM was registered on the flow meter at 100 PSI PDP

The TFT automatic flow increased to 150 GPM at a PDP of 180 PSI

It is fair to say the TFT performed as expected.  The nozzle did what it is designed to do in both tests, adjust its baffle to make a usable stream with the given inlet pressure and flow.  It worked "wrong" at first because we used it "wrong" at first.  We knew that would happen, but we want you to know it, and we want you to see it.  If you run the math based on old school theoretical values, the TFT should have been pumped at around 170 PSI.  The piping loss would result in about 10 PSI extra, putting us at the 180 PDP we got.  I expected the pressure to be a bit lower with the larger ID of the hose, but the slight variables in the testing equipment, piping and flow meter cannot pinpoint the actual number, nor is it necessary to.

Test 2.  

The nest test subject was the 7/8" smooth bore at 100 PSI PDP.  The stubby Akron tip was attached to a standard Akron full ball valve shutoff.  We noted a flow of approximately 120 GPM on the flow meter, with the use of a handheld pitot tube, we got a reading of approx 32 PSI (124 GPM) which corresponds to the flow meter with only a 4 GPM difference.  The hose was expectedly soft at the nozzle inlet and prone to kinks without care being used but the stream of water delivered was still effective with a decent reach and continuity.  

The 7/8" tip yielded 120 GPM at 100 PSI PDP

The 7/8 Tip was increased to 150 GPM, and we noted a 145 PSI PDP.  We recognized the tip was 10 GPM under pumped, but we wanted to keep the flows equal from nozzle to nozzle.  The net improvement from test 1 to test 2 was a gain of 35 GPM by switching nozzles and using the same PDP.  The nozzleman had no notable issue controlling this hoseline in either test.

Test 3.

The last test subject was the Elkhart SM-30 Automatic nozzle.  We expected similar results to the TFT.  The automatic nozzle had a usable stream and was manageable for the single firefighter holding it in the first part of the test.

The Elkhart SM-30 yielded 75 GPM at 100 PSI PDP

When we performed the SM-30 test, the results ended up surprising me.  It flowed 10 GPM less than the TFT at 100 PDP.  When we boosted the pump pressure to achieve 150 GPM, it required a PDP of 160 GPM.  This was certainly more favorable than the higher 180 PSI for the TFT.  The nozzleman had more difficulty controlling this hoseline at 150 GPM

The test results are good data to review.  Please remember to do your own testing and verification.  I want to remind everyone we did not evaluate these nozzles for the sake of creating a matched hose and nozzle system, but simply to see how they would perform when improperly pumped as well as properly pumped.

When looking at all 3 nozzles, it is apparent that the smooth bore was more forgiving with low hoseline pressures and can be expected to provide the highest flow under such circumstances, regardless of the reason for the low pressure.  This is an important factor you should consider.  The 7/8" tip yielded 35 GPM more than the TFT and 45 GPM more than the Elkhart at 100 PSI PDP.  If we tested a low pressure fixed orifice combination tip, we could expect some very similar results to the smooth bore.

In summary, I urge you to carefully consider your hose and nozzle setup and consult with experts oin the field of this science.  Sales associates aren't always as educated as you trust them to be, and it is important to seek out your own information and set up testing.  It is even more critical to assure you're pumping the proper amount of water when performing structural firefighting.  The minimum goal you should aim for is 150 GPM, as it represents a flow that has been proven to have effective fire knockdown power and is manageable for a 1 or 2 person nozzle team.

I wish to extend a thank you to the firefighters I work with for their assistance gathering this great data.  Please feel free to comment on the Facebook page.

-Mike G.