APPARATUS SPECIFICATIONS SHOULD INCLUDE PIPING DETAIL
APPARATUS/EQUIPMENT
Senior Vice-President
Apparatus specifiers should thoroughly understand their department’s current operating tactics for water delivery, as well as those that could be used in the future, before completing specifications for new apparatus. Unfortunately far too many pumpers are being built today to standards for water use developed 30 years ago. One vital area, piping for both intake and discharge lines, must now get some long overdue attention.
The time to meet future needs with apparatus is during the specification writing. Piping of a pump can be done to achieve tactical objectives if the desired flows, both current and anticipated, are known. First, let us discuss the discharge piping for preconnected lines.
It used to be that the only preconnect we had was a booster reel, with a ¾-inch supply pipe that probably had eight to ten elbows between the pump and the reel. This was a carryover from the chemical engines that discharged about 25 to 30 gpm. Today, most fire departments have standardized on 1 1/2-inch preconnects generally located at or near the pump panel and designed to deliver 95 to 125 gpm. Connections to the pump include 1 ½-inch pipe and two or three elbows. This is OK until the new captain decides to use 1 ¾ or even 2-inch hose.
If his department intends to use 1¾ or 2-inch preconnects, the standard 1 ½ -inch piping will probably severely restrict the ability to deliver the desired flows of 200 to 350 gpm. When specifying, 2-inch or even 2½-inch pipe and valving for these preconnects (with a minimum of elbows) will not greatly increase the cost but will certainly ensure adequate water flows with minimum internal piping friction loss.
Rear discharges can be very useful for 2½-inch or larger preconnects, but you should be aware of how apparatus builders get the pipe to the rear of the apparatus. Some are very direct in that the pipe goes straight to the rear with only one elbow and a valve in the line. Others are just short of horrible! Five, six and even seven 90-degree elbows are used to snake the piping from the pump to the rear discharge. Some manufacturers weld the pipe directly into the tank; some sleeve the tank before inserting the pipe; and still others go above, below, or beside the tank.
The next time specifications are written consider the alternative of terminating rear preconnects at the front of the hose bed at east 3 or 4 inches above the flooring to allow clearance for hands and wrenches. This will eliminate long piping runs, reduce the number of elbows, reduce the number of times the tank is penetrated, and it will probably lower costs. The loss is about 10 feet of hose (which is in the bed) but that really should not be a problem. If rear step discharges are a necessary part of the department operations, oversized piping can and should be used.
On the suction side of the pump, piping losses are much more critical. And . . . there are really some plumbers’ nightmares in this area. Admittedly, fire departments often ask for these problems when they specify two auxiliary suction valves, a suction-side relief valve, and a 4-inch Storz inlet, in addition to the main pump inlet, all on one side of the apparatus.
Front and/or rear suction lines coming into the pump can further complicate the plumbing. Notwithstanding these special requirements, here are some helpful suggestions to keep you out of trouble.
- Specify full flow valves for all suction requirements: 2½-inch valves for up to 500 gpm; 3-inch for higher flows. The main suction tube should be used for flows over 800 gpm.
- Behind the valve specify one long sweep elbow or at least only one 90-degree between the valve and the pump. This provides a smooth path for the water and reduces the incoming friction losses.
- Use a 3-inch tank-to-pump line and valve. If possible, specify no elbows be used outside the tank. For higher flows (over 500 gpm) for multiple preconnects and mounted deluge guns, dual tank suction lines may be necessary.
- Specify a check valve in the tankto-pump line. This valve could prevent a costly (and embarrassing) tank rupture.
Specify a suction side relief valve whenever the pumper could be used in a relay. These are generally preset at 100 or 125 psi and dump water to the street when incoming pressures exceed this.
Front or rear suctions are very handy for fireground operations, but specification writers should understand a few facts before including one or both.
They are expensive. Front suctions with an air-operated valve can cost as much as $300 depending on the chassis.
Either front or rear suctions will be limited in the amount of water they can draft.
A free 37-page Apparatus Specification Manual, designed to alleviate some of the work in drawing up precise pumper specifications, is available from W. S. Darley & Company, 2000 Anson Drive, Melrose Park, III. 60160 (telephone: 1-800-3230244).
Each section of the manual presents examples of possible specifications for every part of the apparatus, from body construction, electrical systems and hose reels to custom options, pumps and standard chassis features. Also included is a sample of instructions to bidders.
With up to 10 elbows in a 5-inch line, it stands to reason that considerable friction loss will be encountered at high flows. In general, welded pipe construction offers the minimum friction loss in suction piping.
Rear suctions, particularly those 4-inch or larger, take up considerable space. This could result in reduced compartment size, a higher hose bed or a reduced water tank capacity.
Last, but certainly not the least important especially to the one who has to maintain the apparatus, is the access to the plumbing particularly in the pump compartment. This is one area where considerable time should be devoted to seeing what is available from the various manufacturers. If maintenance people take part in writing the specifications, they will want easy access.
Newer apparatus have been provided with doors inside the locker compartments, above the pump on either or both sides, or (and this is the ultimate) entirely across the truck under a top-mounted pump panel. Even an easily removed plate or grate above the pump would be of some help. Time is money and the quicker an apparatus pump and piping can be serviced, the cheaper and better it will be for all.
In the future when developing specifications be sure to consider the too-longoverlooked piping. Determine local needs, set the performance flows required, and write them into the specfications to assure that present and future needs will be met. Ample flows into and out of the pump can be obtained to meet requirements when proper piping is designed into the apparatus.
