Pump Talk

by Gary Handwerk

Too Many Discharges Are An Expensive Mistake

Designing fire apparatus with more discharge outlets than necessary not only adds cost but, more importantly adds complexity. Nobody needs more controls and gauges making the pump operator’s panel more complicated and harder to operate at 2 a.m. in a snow storm when no one is functioning optimally.

On top of that, the added controls and gauges take up space, which, undoubtedly could be used for something far more useful. Additionally, all the extra valves, controls and gauges will eventually need servicing or repair. We have all seen inside some pump compartments that look like cans of worms. That’s what happens when there are lots of outlets.

What amazes me is how many apparatus I see across the country with 13, 14, even 15 discharge outlets. Is this a status symbol? Maybe it is a poor understanding of National Fire Protection Association 1901 requirements. Maybe there are legions of miniature mechanics looking for work in tight places. Now don’t misunderstand me, if you need handlines for 20 firefighters, go for it.

There are some minimum discharge requirements in the NFPA 1901 standard for a rated pump. Those requirements are:

• Two preconnected line connections fed by 2-inch valves and piping.

• A tank refill gated line.

• At least two 2.5-inch outlet connections.

• Enough additional 2.5-inch or larger outlet connections to total, or exceed, the capacity rating of the pump.

In other words, for a 1,500-gpm pump, the total of all discharge flow rates must be at least 1,500 gpm. NFPA 1901 contains a chart that sets flow rates for various outlet sizes. For instance, the NFPA flow rate for a 2.5-inch outlet is 250 gpm.

Outlets less than 2.5-inches are not counted, and a deck gun itself is not counted, but the base of the monitor where the stream straightener screws on can be counted as a 2.5-inch or 3-inch hose thread connection. Also, the fixed waterway on an aerial is rated at 1,000 gpm only.

You’ll notice I talk about outlet connections. That’s because NFPA only counts the first permanent hose connection on the apparatus. It doesn’t consider the valves or piping size. Additionally, detachable adapters, fittings or valves do not count either.

The reason NFPA 1901 only counts the first permanent hose connection is because the intent was to make sure the apparatus has sufficient capability to relay the pump’s rated capacity 1,000 to 1,200 feet down the street to supply another pumper. 

To do this, you can use multiple 2.5-inch hoses or just one large diameter hose (LDH) or a combination. The limiting factor is the loss in the hose. This explains why the NFPA outlet flow rating looks so low – NFPA really counts hose size. These ratings keep the velocity (the friction loss also) in the hose low; the velocity used is 16.33 ft/sec. The formula to calculate velocity in feet per second is: V = (.3208 X gpm)/area of pipe or hose (square inches).

The first permanent connection indicates the original designers intended usage and flow expectations. Adapters can be added after the fact with no thought to the original design.

Many pump operators already know a typical side 2.5-inch discharge with only a 2.5-inch valve will flow more than 250 gpm. Depending on the pump model and piping, a 3-inch discharge and valve can flow 1,000 gpm with very low internal loss. A 4-inch discharge/valve can flow well over 2,000 gpm, again depending on piping and pump model.

So, you can have a 3-inch valve and have a 4-inch or 5-inch permanent hose connection and get the 525 gpm or 1,000 gpm NFPA rating and easily meet the flow requirements, assuming the piping and pump model are correct.

It’s possible to build a rated 1,500 gpm apparatus with only:

• One 1.5-inch tank refill with a 1.5-inch valve.

• Two 2.5-inch connections with 2.5-inch valves.

• One 5-inch connection with a 3-inch valve.

• And two 1.5-inch preconnections with 2-inch valves.

That’s six connections or valves, and even if the department adds a bumper jump line, a 2.5-inch preconnect line and a deck gun, that’s still only nine outlet connections.

What seems to happen is some fire truck sales staff or some truck builders believe they need lots of free side or rear 2.5-inch discharges to meet NFPA requirements.

So, instead of just the nine outlets like above, departments have four additional 2.5-inch outlets for a total of 13 outlets.

The big question is: are the four extra 2.5-inch discharge outlets really necessary in addition to the preconnects, the two 2.5-inch outlets required by NFPA and LDH outlets?

I can see two additional 2.5-inch discharge outlets at the rear of the hose bed, one with 300 feet of 3-inch hose with 2.5-inch couplings connected to a 500 gpm personal monitor and the other one with 300 feet of 3-inch hose with 2.5-inch couplings connected to a water thief used as an apartment feed line.

If you add these two lines to my example apparatus above, you have 11 outlet connections. You could also use the two required 2.5-inch outlets for these rear discharge applications and be back down to nine outlets.

The moral of this story is to not buy discharge outlets that you will not use.

I must note that when I write about NFPA requirements and their meaning, I’m expressing my personal interpretation of the requirements. Only the NFPA can make formal interpretations.

In the future, look for an article discussing the internal discharge loss in pumps, pipes and valves.

Editor’s Note: Gary Handwerk is global pump product manager for Hale Products. He has been involved with the fire service industry for 36 years working for various fire apparatus or pump manufacturers and has been a member of the National Fire Protection Association (NFPA) Fire Apparatus Standards Committee for 15 years.