URBAN PUMP SERIES (EP 03) - THe INTAKE SIDE OF OUR PUMPS

Urban Pump Series
Part 1 - Getting Water
Episode 3 - The Intake Side of Our Pumps

The Intake Side of Our Pumps

The Intake Manifold

Every Driver Engineer needs to understand how the intake side of our pumps is connected behind the panel.

To help teach our younger members here in Dallas, I like to jump on the whiteboard at the station and draw some version of the following diagram...

Note: The above illustration represents the INTAKE SIDE of our pumps. It's important to understand that this is only the intake side... not our discharge side.

Although the physical pump itself is much more complicated than this simple illustration, it usually helps our members visualize what is happening as we begin to move water into our pumps. Typically, I'll label A, B, and C with the intakes from our actual apparatus. For example, Intake A would be one of our 2 1/2" Pony Suction Intakes. Intake B can represent one of our 5" Keystone Intakes, and Intake C represents the other 5" Keystone Intake.

Note: While we only show three intakes in this illustration, our Dallas Engines are outfitted with 5 intakes:

5" Keystone (Driver Side)
5" Keystone (Officer Side)
2 1/2" Pony Suction (Driver Side)
2 1/2" Pony Suction (Officer Side)
Tank To Pump Intake
- Note - the Tank To Pump Intake should have a check valve that allows water to flow out of the tank into the pump, and prevent water from being pushed back into the tank.

What's important to gather from this illustration is that as water comes in on Intake C, it collects in the intake manifold BEFORE it enters the pump. In fact, all three intakes feed this manifold before water enters the pump.

Why is this important?

Our pumps can only take in a limited amount of water at a given time. Any excess water fills the intake manifold and pushes back against the intake valves at hydrant (or tank water) pressure.

Note the highlighted intake manifold in the image below:

Let's say Intake C is connected to that hydrant with 80psi of static pressure (nothing is flowing on our discharge side). If we were to open Intake B (which we said was one of our 5" Keystones), what will happen?

Water will exit at roughly the same pressure that it came in on from Intake C.

Once we've gone over all this on the white board, it's time to head out the engine and illustrate this off tank water...

Important - As mentioned above, the Tank To Pump intake should have a check valve preventing water from flowing back into the tank. It is a one-way system. Therefore, opening the tank to pump will not refill your tank if you are connected to a permanent water supply (i.e. hydrant). If you do have water pushing back into your tank, you need to contact your shop/maintenance division and have them look into this.

The Foundation For Dual Pumping

The reason that all this is so important for Drivers to understand is that this forms the foundation for Dual Pumping. And although we won't dive into this topic today (it's coming in a couple more episodes), I'll share how the illustration plays out once we start talking about two engines sharing the same hydrant's volume and pressure.

Here is a brief layout of Dual Pumping from our Pump School with Rick Brewer:

The Attack Engine makes the fire
The Second Due (Back-Up Engine) catches the hydrant and forward lays the supply line to the Attack Engine.
Once the Attack Engine has its permanent supply, the two Drivers work together to lay a 3" supply line INTAKE to INTAKE to create a redundant water supply. This allows the Second Due Engine to become a backup in the event of a catastrophic failure with the Attack Engine's pump.

Understanding Your Intake (or Compound) Gauge

Compound... What?

An often misunderstood word/phrase for the urban firefighter is "Compound Gauge." If you do a quick survey, I will bet that most of urban firefighters will tell you that the Master Discharge is the same thing as your "Compound Gauge."

"Technically..." they aren't wrong since most manufacturers repurpose the same gauge for BOTH the Pump Intake and Pump Discharge. But, in practice, they are incorrect in thinking that the Pump Discharge is a compound gauge.

The Compound Gauge refers to your Master Intake Gauge, and the reason it is called a Compound Gauge is that it combines two different gauges into a single display.

The first gauge is the one every urban firefighter is familiar with, the pressure gauge. Pressure gauges utilize PSI (pounds per square inch) as their unit of measure and consume 99% of the dial.

But you'll also notice that below the 0psi pressure marking, we have an entirely different measurement system... -30 inHg. This is your Vacuum Gauge used to measure force in inches of mercury (inHG) while performing drafting operations.

Why do I bring this up? Well, at the bare minimum, I can possibly save you a bit of embarrassment if you're ever asked what's on your Compound Gauge at a fire, and you mistakenly give the Master Discharge Pressure.

Simple mistake for the guy who never drafts and couldn't suck water out of a pond if my life depended on it. Sure, I probably read this at some point in my promotional studies, but like every other piece of "useless knowledge." Like most of us, I glossed over the drafting sections in my Pump Operator book because I felt like it didn't apply.

In all seriousness... it's about knowing our equipment and ensuring we use common terminology.

The Most Important Gauge On Your Panel

In my opinion, your Compound/Pump Intake Gauge is the most important gauge on your panel. Why? Because it holds the answer to your remaining water supply at a working fire. It can tell you a lot if you know what to look for.

Tracking Water Supply

There are two main ways most firefighting publications (articles, books, etc) offer as a means to determine the remaining water supply that we have on the urban fire ground (permanent water supply via municipal hydrant system):

1. Percentage Method

To calculate the remaining water supply using the Percentage Method, you'll need to calculate the drop in pressure (between the Static and Residual) on your intake gauge as a percentage.

For example, if you have 80psi Static Pressure and then open a deck gun flowing 500 GPM with 60psi Residual... it would equate to a 25% drop in pressure.

Once you know that percentage, you can run it against the following matrix:

0-10% = 3X initial target flow
11-15% = 2X initial target flow
16-25% = Same as initial target flow

So, in the above illustration, you would have roughly another 500 GPM available for firefighting operations.

2. First Digit Method

To calculate the remaining water supply using this method, note the difference between the Static and Residual Pressure. If that difference is less than or equal to the first digit in the Static Pressure reading, the theory says you can provide three times your initial target flow.

If the difference is less than or equal to two times the first digit, you should be able to provide two times the initial target flow.

And lastly, if it is less than or equal to three times the first digit, you should be able to provide the same initial target flow.

Again, here is the matrix:

Less than or equal to the first digit = 3X
Less than or equal to 2X first digit = 2X
Less than or equal to 3X first digit = 1X

My opinion... none of these are remotely practical when the sh*t hits the fan.

When we pull up at a three-story, 24-unit apartment complex with a working fire on the third floor that has extended into the attic, I don’t see any of these as practical. There is simply too much going on and too much being demanded from our Engineers to run these formulas.

So what can we do? Practically.

Before I share a simple method that I was taught as a young FRO, I need to make this simple and important disclaimer - I recognize and admit that this is a flawed system/method. There will be a number of you, who are far smarter than I, that will be able to poke all sorts of theoretical holes in this. Technically, I don’t disagree with you. BUT, I also can say with confidence that I’ve used this method with a great measure of success. The key is for you to get out and flow water on the training ground to see if you achieve similar results.

"Hashing Your Intake"

To utilize this method, start by noting your Static Pressure. You can do this mentally or by creating an actual “hash mark” on your intake gauge with a wax pen (like you see in the image below).

Next, open the desired discharge and note the Residual Pressure. What’s important here is to know your target flow. In fact, without a knowledge of your target flow, none of these methods work.

The difference in pressure between Static and Residual becomes the "cost of doing business" for additional lines that match your initial target flow, up to 1,000 GPM with a single 5" supply line.

Here is an example:

Static Pressure = 85psi
Residual Pressure = 70psi while flowing 500 GPM.

Using this method, you can anticipate that for every 500 GPM you put into play, it's going to cost you 15psi... up to 1,000 GPM with a single 5" supply line.

Why do I keep mentioning “up to 1,000 GPM with a single 5” supply line?”

The simple answer is… friction loss on the intake side of your pump (in your supply hose). The reality is once you start pushing over 1,000 GPM on the discharge side of your pump, you start to see a major jump in friction loss in your 5” supply hose, which will translate into larger drops in pressure on your intake gauge.

If we are under 1,000 GPM, you'll notice that our friction loss in 100' of supply hose is between 0 and 6psi. Once we move into the 1,250 and higher flows, we see a significant rise in our friction loss curve.

So, the easy way to combat unnecessary friction loss in our supply setup is to drop a second 100' of 5” to our hydrant and run it off of another [hydrant] discharge. Because we've split the volume load between two 5" hose, our friction loss for the same 100’ distance looks like this now...

We've effectively doubled our volume on the discharge side and kept minimal friction loss in our supply hose setup. Why does this matter? Because if we don’t address the rapid increase in friction loss above 1,000 GPM, this method will quickly run away from itself as we put increased volume into play. Once you have a second supply hose connected, you're back in business, up to 2,000 GPM.

Now, it's important to note that the friction loss in our supply hose is only part of the reason that we see a difference in Static and Residual pressures. Another factor is our municipal water system’s volume capacity and demand. Despite this and additional considerations, I’ve used this hashing method very consistently over the past decade since it was taught to me.

A few things we need to be mindful of as we wrap this up:

Always leave yourself margin. This is not an exact science.
I'm a fan of charging lines hot to assist with pushing out kinks in the line. As I begin to move closer to 20psi on my compound gauge, I will be much more cautious as I pull levers, keeping a close eye on my intake gauge. This should be done regardless of discharge volume.
There is no set drop between Static and Residual that you can anticipate every time. There are too many variables to create “a crosslay flowing 160 GPM will always result in a 5psi drop” rule of thumb. Every hydrant will be different.
Train, train… and then go out and train some more. See if this works for you. If not, test and practice the initial two methods we describe so that you can effectively deploy them when the bell actually hits.

CONCLUSION

Water Intake is the foundation of water supply. We must understand how water comes into our engines and can be pushed back out of additional intakes if the valves are opened.

We also want to encourage you to discuss these with the Senior Engineers and members at your station. There is a wealth of knowledge beyond what we're offering here that these guys/girls have that you can tap into and learn from.

Until next episode...

Hold fast & raise the bar,

DISCLAIMER: Dallas Fire-Rescue does not endorse or necessarily promote these videos. The information herein is my best understanding of the material covered and the subsequent views expressed are my own and not necessarily those DFR. These videos are strictly for educational purposes only. It is critical that you follow your department's MOP/SOP, and talk with your Station Officer (and crew) before implementing anything you see here on The Roll Steady.