Filtered Water: Use a strainer to perform simple pump preventative maintenance

By Patrick Pauly

Regardless of where your rural fire department operations occur, if you have to draft water, you should attach a strainer to the end of your hard-suction tube. Taking a few extra minutes to do this will pay dividends in the long run.

Many different types of strainers are available, and many manufacturers offer models with their own features. In this article, I’ll take a closer look at the reasons for using a strainer and the different styles available today.

Pump Hazards
Most fire service personnel and pump maintenance people agree that a strainer reduces the number of large items that can get lodged in your pump. Often, leaves and plants float or grow in the water we’re attempting to draft. But many things can get through the hard tube and into the impellors or “heart” of the pump, such as twigs, small stones, cans, small bottles, leaves, plants and pieces of plastic. A screen on the intake connection at the pump will stop most of these items, but some can slip through. Even with a screen in place at the intake connection, items that enter the tube may collect on the screen. This could possibly cause less water to enter the pump, eventually creating a condition known as cavitation.

Cavitation (a subject I’ll discuss more in a future article) is extremely dangerous for the interior of your pump. It occurs when you attempt to discharge more water than is available through the intake. This results in a rapid heating of the pump’s internal parts, which damages the pump—and that means paying a lot to fix it or replace it.

Strainers help prevent items from getting into the pump by stopping them a distance away from the actual pump, but they can’t guarantee protection from cavitation. This is why the pump operator or other people at the water operating site must pay close attention to make sure cavitation doesn’t occur.

What to Look For
The pump operator must watch the discharge gauges, intake gauges, tachometer and sound of the apparatus while drafting. A change in any of these elements might signal a blocked strainer.

Simply looking at the area immediately around the strainer may help you determine if there’s a problem. Items swirling around, floating past or sticking to the hard tube may be an indication that similar items are sticking to or clogging the strainer. If water is moving rapidly, it’s less likely that there’s a problem with clogging.

You may not expect blockage to be a problem when you’re drafting from a portable holding tank. However, the water came from somewhere—and it may be loaded with items that got into one or more tankers because the source engine at the fill site didn’t use a strainer.

In cold weather, another problem can occur: the formation of ice on the strainer. The surface of moving water may not be frozen, but the holes in a submerged strainer could freeze if allowed to sit stationary for too long. To prevent this, the operator or other persons should occasionally lift the tube and strainer from the water to ensure ice isn’t forming. If you don’t take steps to alleviate this issue, water flow could be significantly reduced or stopped.

Strainer Types
Most fire apparatus manufacturers will provide a basket- or barrel-type strainer with any new unit that’s equipped with a pump. These devices work well when the water is deep enough that there’s 8 to 15 inches of water above the submerged strainer. However, water of this depth is sometimes not available, as is often the case when drafting from a moving body of water, a collapsible water tank or a static body of water like a swimming pool or pond. And without enough water to cover these strainers, the floating strainer or low-level strainer become more attractive.

A floating strainer actually floats on the surface of the water, while a low-level strainer sits on the bottom of the water source. Both are equipped with a hinge or swivel to allow for different angles.

Floating strainers are very effective at preventing blockages, but they can puncture collapsible tanks if they’re not fastened to several points and are allowed to strike the sides of the tank during operations. Another potential issue: Some low-level strainers have been found to be restrictive, as they are not constructed to allow the same water flow capacity as other strainers.

Like other equipment you use, select a strainer according to the manufacturer, model and performance, such as flow capacity. Although they’re screwed onto the end of the hard tubes, it’s a good idea to attach a rope or line to the strainer. This allows for a safer and easier deployment and recovery of the strainer and tube during most drafting operations. That rope can also assist with keeping a barrel- or basket-type strainer off the bottom of the water source. Additionally, using two ropes should stop the strainer and tube from floating back and forth and punching a hole in the tank side.

Strainer Standards
Strainers are addressed in several NFPA standards, including NFPA 1901: Standard for Automotive Fire Apparatus. But exactly how these precious devices are used depends on you and your department.

Maintenance is relatively simple. Always refer to the manufacturer’s recommendations. Regularly inspect the gasket in the female-swivel connection, and replace these gaskets as necessary, especially if you discover any cuts, tears, nicks or worn areas. Some departments will remove and re-install a gasket upside-down when that gasket shows slight wear. This may or may not be OK. My recommendation: Don’t take a chance on something as inexpensive as a gasket; you don’t want to be disappointed later by a failed drafting operation. A bad gasket can easily result in an air leak and a failure to draft water.

Additionally, some strainers, such as a low-level or floating strainer, may require some type of lubrication at hinges or swivel points. Be careful to follow manufacturer’s recommendations for the correct type and amount of lubrication.

In Sum
Strainers are a simple way to make drafting operations safer, more efficient and less likely to fail or experience pump problems. Use a strainer during any fire department activity for rural fireground operations when drafting, whether it’s an actual emergency or a drill. And don’t forget to routinely monitor your operations and always work safely.

Pat Pauly has been on the staff at the Pennsylvania State Fire Academy (PSFA) in Lewistown as a resident instructor since 1988, where he supervises 80 part-time adjunct instructors for the resident and academy on the road programs. He became a state fire academy instructor in 1978 and has taught throughout rural Pennsylvania since the 1980s. He holds an associate degree in computer science technology and is nationally certified as Firefighter III, Fire Instructor II, Fire Officer II, Driver/Operator Pumper and Driver/Operator Rural Water Supply. Retired as deputy chief from the Lewistown (Penn.) Fire Department after 31 years, Pauly is active with the West Granville Fire Company in Lewistown and Granville Township.

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Comment by Oldman on July 12, 2009 at 4:00pm
Excellent points. We don't draft as much as other departments might, but the strainer is a must. Our biggest issue with drafting is not usually the bigger items which as you point out are usually controlled with the strainer on the hard suction and at the pump intake, but the sand and silt which will be picked up with a drafting operation. The sand can do extreme damage to the impeller. A thorough flushing with fresh water after any drafting operation.

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