Adams, Apparatus, Apparatus Purchasing, Pumpers

Apparatus Purchasing: Flows and Rear 2½-Inch Discharges

Issue 9 and Volume 25.

BY BILL ADAMS

Some comments can stimulate challenging the status quo, cause creative thinking, and provoke violent disagreement. One example: “2½-inch discharges are often underutilized, occasionally misused, and generally misunderstood.”

Another: “Most pumpers are ‘overdischarged,’ especially in the 2½-inch category.” Overdischarging means the total capacity of the discharges far exceeds the pump’s capacity regardless if operating from draft or a pressurized source. Yet another: “Despite innovations in tactics, hose sizes, and the use of multiple preconnects, apparatus are still purchased with numerous 2½-inch capped discharges serving no direct purpose except collecting dust and fingerprints.”


Related Content


Apparatus manufacturers (OEMs) historically provided a 2½-inch discharge for each 250 gallons per minute (gpm) of pumping capacity. Leader-line wyes or reducers were attached to them when 1½-inch hose was introduced. After preconnects became popular, separate valving was supplied for them. With today’s large-capacity pumps, there may be more than a dozen discharges of various sizes on a pumper.

This predelivery photo of the Providence (RI) Fire Department’s Engine 7 shows two rear 2½-inch discharges furnished with leader line wyes—common in Rhode Island. Some companies will preconnect one outlet with a common length line and leave the other open to “pull and break” the length desired. Others preconnect both outlets. Before putting into service, most rotate the wyes 180 degrees to protect the handles

1 This predelivery photo of the Providence (RI) Fire Department’s Engine 7 shows two rear 2½-inch discharges furnished with leader line wyes—common in Rhode Island. Some companies will preconnect one outlet with a common length line and leave the other open to “pull and break” the length desired. Others preconnect both outlets. Before putting into service, most rotate the wyes 180 degrees to protect the handles. (Photo courtesy of Greenwood Motors, E-ONE dealer for Rhode Island.)

This Seagrave has six 2½-inch rear discharges, each NFPA 1901 rated at 250 gpm, although actual flows can be much higher. Regardless if piped or valved with 3-inch, the first “hose thread” off the pump determines the rating.

2 This Seagrave has six 2½-inch rear discharges, each NFPA 1901 rated at 250 gpm, although actual flows can be much higher. Regardless if piped or valved with 3-inch, the first “hose thread” off the pump determines the rating. (Photo by author.)

3 A typical British pumping appliance showing all discharges and inlets in the rear compartment. The rig has one 2.76-inch (70-mm) supply line coming in and one going out. (Photo courtesy of Andy Daley, Liverpool, England.)

ISO, NFPA, AND RATINGS

Before addressing 2½-inch flows, ratings should be explained. Some apparatus purchasing committee (APC) members may not be well versed in capacities, flows, and ratings. Judicious vendors will sense that. It is their obligation to educate APC members—albeit subtly, so as not to offend. One criterion used when the Insurance Service Offices (ISO) rates a community’s fire protection is the pumping capacity available on a prescribed number of National Fire Protection Association (NFPA) compliant apparatus. The ISO says what you need for a rating, and the NFPA tells you how to achieve it.

NFPA 1901, Standard for Automotive Fire Apparatus, Table 16.7.1 rates discharge outlets by the size of the first “fire hose” thread off the pump and not by the valve size. They include 2½-inch at 250 gpm, 3-inch at 375 gpm, 4-inch at 625 gpm, and 5-inch at 1,000 gpm.

REALITY

NFPA 1901 Annex A sentence A16.7.1 says: “A 3-inch (75-mm) valve can easily supply a 5-inch (125-mm) connection at 1,000 gpm (4,000 L/min) with little noticeable loss through the valve and pipe.”

Many OEMs claim 1,500 gpm is readily achievable from a midship pump’s side 3-inch side discharge. Those 1,000-gpm and 1,500-gpm flows might not be attainable when piped to the rear with 3-inch pipe and numerous elbows and fittings. The NFPA specifies discharge rates—not the flows or the pipe sizes to achieve them. Ratings do not extinguish fires. Water does.

If flow requirements are not in writing, they do not exist. Should purchasers rely on a vendor’s verbal assurance of flows? Do you trust the expertise and professionalism of every OEM’s plumbing and engineering staff? Attaching a large-diameter hose (LDH) adapter to a 2½-inch discharge does not guarantee actual flow. A written performance requirement in purchasing specifications and third-party certified testing will.

REAR 2½-INCH DISCHARGES

Specification verbiage describing rear 2½-inch discharges includes a 2½-inch valve with 2½-inch piping, a 2½-inch valve with 3-inch piping, and a 3-inch valve with 3-inch piping. Most piping terminates with iron pipe threads (IPT) and usually an adapter with a 2½-inch male hose thread. If the first hose thread from the pump is 2½-inch, the NFPA rates the discharge at 250 gpm—regardless of the actual flow. If achieving an ISO rating is significant, using a 3-inch IPT by 3-inch hose thread adapter increases the rating to 375 gpm. While 3-inch adapters are common, wyes and elbows with 3-inch hose threads may be hard to find.

It is strictly the fire department’s business if rear discharges supply a ground monitor, a wye feeding two small handlines, a single large-volume handline, or a sprinkler/standpipe fire department connection. It should inform vendors of the intended usage and flows desired. It’s the vendor’s “moral” obligation to design the discharge accordingly. If the flow requirement is in writing, it becomes the vendor’s legal obligation to do so.

Wyatt Compton, product manager for the REV Group’s Spartan Emergency Response division, was asked to comment on flows from rear 2½-inch discharges. “A discharge piped and valved 2½-inch could flow between 300 and 500 gpm,” he says. “Valved 2½-inch and piped 3-inch could be between 500 and 750 gpm, and 3-inch all the way could be between 750 and 1,250 gpm.” Why the variance? Compton says, “Contributing factors are the number of elbows and fittings, hard pipe or flex hose, groove or threaded pipe connections, how the discharge manifold is designed and piped, if the discharge has a foam check valve, if it has a flowmeter with a short run, and the actual distance from the pump to the discharge. Those factors, especially when combined, can significantly affect flows.”

TESTING

It’s dangerous for firefighters to advance a line of any size from a rear discharge into a situation expecting to flow a certain gallonage—and not having it. Ditto for expecting certain flows to ground monitors and fire department connections. Purchasers should consider “third-party-certified testing from draft” to verify the flow from rear discharges that vendors claim they can get. The same is applicable for front bumper discharges.

Compton states, “For a manufacturer, it would be simple enough to do the testing from draft. I’m not 100 percent sure it needs to be from draft because downstream of the pump, ‘pressure is pressure.’

“It’s definitely an option as 2½-inch can have a WIDE array of flows. With the advent of the small ground monitors that may be supplied by a single 2½-inch hose, it’s quite reasonable for customers to verify which discharges have the required 500-gpm flow available.”

Compton continues: “Manufacturers will always err on the large side, especially if the flow is a specification requirement. Most often, I prescribe to the idea of a ‘maximum acceptable pressure loss’ measured from the pump to the discharge outlet. Specify a specific flow and a maximum of 10 pounds per square inch (psi) pressure drop from the pump to discharge thread, and let the manufacturer decide how to plumb it. Three examples from Chicago (IL) Fire Department specifications are: ‘All flow for the 4-inch LDH discharges must show no more than 10 psi loss between pump and discharge connection at 1,000 gpm of flow. Crosslays shall be capable of flowing 200 gpm with a maximum loss of 10 psi. The piping will be adequately sized to flow 800 gpm with a maximum loss of 10 psi between the pump and the discharge orifice of the deck gun.’ This takes out of the equation the size of hose used for testing and makes it fairly repeatable for most situations.”

Close examination of the panel shows eight discharge pressure gauges. There is a trash line; a preconnect discharge in the main hosebed on the right side; and two speedlays, one located each side at the lower rear tailboard behind drop-down doors.
This innovative Canadian product merges the European rear pump concept with an American rear-mounted pump—a Darley Model PSRH 1500, a 1,500-gpm NFPA pump with a high-pressure booster for simultaneous flows of 100 gpm at 600-psi pump. It has four rear discharges.

4, 5 This innovative Canadian product merges the European rear pump concept with an American rear-mounted pump—a Darley Model PSRH 1500, a 1,500-gpm NFPA pump with a high-pressure booster for simultaneous flows of 100 gpm at 600-psi pump. It has four rear discharges. Close examination of the panel shows eight discharge pressure gauges. There is a trash line; a preconnect discharge in the main hosebed on the right side; and two speedlays, one located each side at the lower rear tailboard behind drop-down doors. (Photos 4-5 courtesy of Fort Garry Fire Trucks, Ltd.)

BRITISH BRIGADES

One design not embraced domestically is having rear-mount fire pumps with a minimum number of discharges. The London Fire Brigade’s roster includes hundreds of pumpers called DPLs (Dual Purpose Ladders). They feature 1,000-gpm (3,910-liter) rear-mount pumps; 360-gallon (1,365-liter) booster tanks; and, except for twin high-pressure booster reels, no preconnected hoselines. There are usually three or four 2.76-inch (70-mm) discharges in a rear compartment. They attach whatever size and length line are required for the incident encountered. This is not a recommendation for the American fire service; it’s merely an observation.

Perhaps they are onto something—rear-mount pumps with a limited number of discharges all off the back end. Other European innovations adopted by the American fire service include rear-mount aerial devices, sexless couplings, LDH, and fully enclosed crew cabs.

Fire department operating procedures are not being questioned. Each should do what is best for its individual response areas. When laying out discharges for a new apparatus, APCs should establish the flow required or that may be required for each discharge. Bear in mind, the apparatus purchased today as a first-due attack rig may end up serving as a supply rig down the road. Discharges should reflect that possibility.

NFPA 1901 does not require a predetermined quantity of discharges. Other than to meet NFPA 1901, vendors do not have the right to tell a fire department how many total discharges they should or have to purchase. Ratings are theoretical. They’re used to meet ISO and NFPA criteria. As mentioned, ratings don’t put out fires. The amount of water that is efficiently delivered through a discharge does.

Disclaimer: My personal belief is every discharge on a fire pump should have preconnected hose attached to it rather than that blind cap collecting dust. It is irrelevant if attack lines, backup lines, leader line wyes, or portable monitors are preconnected or if the preconnects are of various lengths. If the outlets are there, use them. If you don’t need them, why buy them? If an outlet is needed for a nonpreconnected hoseline, what is the difference in removing a cap to attach the hose or disconnecting a hose coupling to do so?


BILL ADAMSis a member of the Fire Apparatus & Emergency Equipment Editorial Advisory Board, a former fire apparatus salesman, and a past chief of the East Rochester (NY) Fire Department. He has 50 years of experience in the volunteer fire service.