Fire pump primers may not be glamorous, but priming systems are critical to pump drafting performance. Pulling a prime quickly is key to fast water delivery, a basic fireground necessity. Last month, we answered several questions about pump priming. This month, we will continue our look at priming...
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Fire pump primers may not be glamorous, but priming systems are critical to pump drafting performance. Pulling a prime quickly is key to fast water delivery, a basic fireground necessity. Last month, we answered several questions about pump priming. This month, we will continue our look at priming systems by reviewing commonly found priming problems. Priming System Integrity
After excessive lift is eliminated as a "no-prime" problem, a recurring no-prime condition can occur due to a variety of reasons. To weed out problems, a good place to start is in the maintenance shop, checking the integrity of the priming system. First, perform cursory checks to see if:
1. There is lubricating oil in the primer reservoir. (If the primer is using an excessive amount of lubrication, check to see if the vent hole in the oil line that functions to prevent a siphon is blocked.)
2. The priming valve is working correctly.
3. The power and electrical connections to the electric primer motor are sound.
Now go beyond that and see what gauge wire is connected to the primer motor/solenoid. How long is the power cable? Is the wire gauge sufficient for its total length in feet versus its amp carrying capacity? (Check with the primer manufacturer for wire-gauge/amp draw/total length requirements.) Does the primer motor have a good ground connection? A primer needs a good electrical supply and a properly sized electrical connection to work correctly and keep on working over time.
In addition to the above items, one reason for not being able to prime the pump is a damaged electric vacuum primer that does not turn, or if turning, is worn and not able to "pull" the required amount of vacuum.
Vacuum Primer Test
To test for a worn or damaged primer in the maintenance shop, isolate the primer by disconnecting the vacuum primer/fire pump tubing connection at the vacuum priming pump. Connect a manometer or master vacuum gauge to the primer. Activate the primer and see how deep a vacuum it will pull. The National Fire Protection Association (NFPA) 1901 guideline is that vacuum primers need to attain at least 22 inches of mercury (in. Hg). See how the vacuum reading stacks up against both NFPA minimum requirements and the primer's original vacuum specification available from the manufacturer. Repair or replace the priming pump as required.
If a no prime condition still persists when drafting from a static water source, air leaks into the fire pump are the likely culprit. Here are some common reasons for air leaks into the fire pump:
- The pump operator left pump discharge, suction or drain valve(s) in the "open" position
- Fire pump suction cap(s) are loose or have bad gasket(s)
- The pump's discharge and suction valves leak, even in the fully "closed" position
- The pump's external relief valve(s) may be damaged and leak
- The pump casing, flanges, and discharge or suction manifold piping have pinholes, the pump shaft seal leaks, the pump shaft packing needs adjustment or a gasket is defective
- Hard-sleeve suction hose has pinholes, has bad gaskets at connections, couplings leak or connections are loose
Pump, Manifold and Suction Hose Assembly Vacuum Test
Once the above causes of air leaks are checked and any obvious deficiencies are corrected, it is a good idea to run a "vacuum test" on the entire pump and suction assembly. To do this:
- Fully charge the truck batteries
- Drain the pump and close the tank-to-pump valve
- Install the suction hose you normally use on the intake of the fire pump
- Cap the end of the suction hose
- Remove all caps from the fire pump's discharge valves (keep the discharge valves in the "closed" position)
- Open all pump suction valves and cap every pump intake opening
- Check and clean out the test gauge connector line
- Connect a manometer to the test gauge connector line
- Run the primer until the vacuum reading is 22 in. Hg (or greater, as stated by the primer manufacturer's original specifications)
- Over the next five minutes, watch the manometer to see if or how far the reading drops