Water pump can be tested with vacuum gauge. Basically two ways to test pump with vacuum gauge. One way involves conducting test without water flowing through pump. Would first insert vacuum gauge into pump’s suction or inlet port. Within 60 to 90 seconds of being turned on, pump should be able to pull vacuum that measures 22.2 inches of mercury on gauge scale (should never run pump without water longer than 90 seconds or pump’s seals may burn out due to excessive friction). Weak vacuum indicates either internal pump damage or leaky seal that’s allowing air to enter pump.

Second way to test pump involves reading gauge while pump pumping water. To do test, must be able to install T fitting at pump’s suction port so water can get past gauge and into pump. Ports on most pumps designed to accept such fittings. One advantage of testing pump this way is that you can inspect water leaving pump. If leaky seal causing low reading, should be able to see air bubbling through water at pump’s outlet. In addition, another T fitting can be installed in outlet port so can measure pump’s outlet pressure. Be aware that volume water pumped by impeller type pump is directly related to how high unit has to lift the water from its source. When pumping water from maximum depth, impeller type unit will pump its smallest volume.


Taking apart a light duty pump—generally water pumps easy to disassemble and repair. Normally can lift pump body from engine after series body screws removed. By removing a couple more screws, can take off volute and expose impeller. Often a single screw will secure the impeller onto its shaft. Pump’s impeller housing can be separated from engine by removing few more screws.

Reverse side impeller will be keyed onto its shaft. Ceramic seal often used on rotating parts of water pumps. Around shaft is ceramic seal’s stationary counterpart that provides mating surface as seal rotates with impeller. The part around the shaft is spring loaded. As the impeller screw is tightened during reassembly, the ceramic seal will be pressed into its stationary counterpart around the shaft. The force from the spring pushing back creates a tight seal between the rotating shaft and the housing.

Ceramic seals break very easily and should therefore be handled carefully. The sharp end of the shaft can easily chip the ceramic material. A lubricant recommended by the manufacturer should be put on the ceramic surface to prevent any heat buildup when the pump is first started and no water is present in the volute to provide lubrication.

Often, screws and bolts become rusted when kept in a water environment. To loosen them, may need to repeatedly apply a rust breaking, penetrating oil over period of several days. Applying silicon grease to the threads of the screws and bolts before reassembly will make servicing the pump much easier next time.

Taking apart a trash pump—some trash pumps can be easily serviced without tools. The front cover of such a pump is removed by turning two quick release hand knobs. When cover is removed, will find that volute looks like the half spiral of a snail or seashell. Part of the impeller will be visible within the cavity in the center of the volute. Water coming from the inlet port flows through the volute until it reaches the impeller. The water and any trash carried with it is thus centrifuged through the volute and out to the pump’s outlet.

Like the pump’s front cover, the volute can be easily removed without tools. This easy access was designed for the pump operator who may occasionally need to free pump of debris that can’t get past impeller. Front cover of pump contains a chamber that mates up with the O ring around the hole in the center of the volute. This chamber channels the water away from the impeller as water leaving the pump. A valve in the pump’s inlet duct seals off the opening at the top of the chamber.

To remove the body of the trash pump from the engine, four bolts must first be removed. This will enable the pump body to be pulled away from engine to fully expose the impeller. Sometimes may be necessary to use a puller tool to remove impeller. Note the large O ring around the edge of the flange on the engine. Along with the bolts that have already been removed, this O ring is used to make a secure seal between the pump and the engine.


1)Be aware that problems with carburetor or engine’s fuel system in general may be result of use old unstable fuel. Also, engine damage could result from operator trying to start engine using ether.

2)Inspect all joints and seals on the pump.

A)Remember that the seals may have been damaged if the pump was ever run without water.
B)The special seal around the impeller’s rotating shaft may need special attention. Be careful not to chip this seal when reassembling the pump. Also, find out if the pump manufacturer recommends greasing the shaft seal when you service the pump, and follow recommendations.
C)A faulty check valve can be responsible for any difficulty priming a pump.
D)If one or more seals between the joints of a pump’s components are defective, the pump may have squirted water onto its engine or electric motor when the unit was previously being used. If the pump’s engine or motor isn’t protected some way, this water could have caused damage. In case of gasoline engine, water may have gotten into the vent on engine’s gas cap. If water was allowed to contact an electric motor, water from a leaking seal may have been responsible for shorting out the motor.

3)Realize that flood water may have gotten into a pump’s engine or motor if the unit was unable to pump fast enough to keep up with the rising water.

4)Look for signs of the corrosion that can result from allowing water to sit in body of pump over period of time. A cast iron pump housing can corrode to form a leak. The point where impeller shaft enters pump body may be especially vulnerable.

5)Inspect the impeller for damage. An impeller can be broken by solid objects passing through the pump. Rocks, wood, other debris could also be stuck in the impeller. If find any debris or evidence damage, may want to install an inlet screen on the pump’s suction hose. The screen would block entrance of foreign materials and thus keep impeller from getting jammed or broken in future.

6)Check the pump’s suction hose or ducting for any defects that may cause vacuum leak.


Light duty water pumps—water pumps generally engine driven, though sometimes pump will be driven by optional electric motor. Well sealed, a pump can pull water from depth of 25 feet to prime itself in perhaps 30 seconds. Once primed, it can lift water 110 feet above the elevation of pump. Able to pump fertilizers and other chemicals without getting damaged.

Water pump is similar to air blower. Each has an inlet, outlet, and impeller that operates in similar way. If air blower leaks, can be annoying but normally no great harm done. If water pump being used to pump chemicals should leak, could be serious, result in hazardous spill that requires special cleanup. To prevent leaks, manufacturer water pump uses several seals (O rings and compressed seals) on unit’s drive shaft.

Impeller of water pump shaped differently than impeller of air blower. Water pump will also have component called a volute which is the pressure chamber that directs incoming water into the impeller. As impeller turns, forces the water through pump’s outlet. Volute also contains a check valve. By sealing the port or duct that forms pump’s inlet, the check valve prevents water in pump from draining back to source.

Jet pumps—another type water pump is jet pump. Jet pump consists of specially designed casing that includes built in jet nozzle. As with standard pump, water enters jet pump’s inlet and is discharged by impeller through the outlet. What makes jet pump different is that some water not discharged, instead recirculated through jet. Water that passes through jet creates a vacuum at tip jet, resulting in additional suction at pump’s inlet. This additional suction helps to draw water into pump. The water drawn into pump once again flows past impeller, and most discharged through the outlet. Remaining water circulates through jet, continuing pumping cycle.

Jet feature is advantage in deep well applications where additional suction needed to lift water from greater depths. However, jet pump needs to be primed with some water before can begin pumping as intended. Many jet pumps lose ability to pump water when air drawn into their impellers. Each time this happens to jet pump, pump must again be primed with some water. Jet pump therefore best suited for use where water level doesn’t drop during pumping operation. As long as no water enters suction line running to water source, jet pump can lift water depth over 100 feet.

Maintaining sealed surfaces and shafts critical to priming and operating jet pump. The inlet check valve, for example, must have tight seal to prevent prime water from draining back through pump’s inlet fitting.

Trash pumps—trash pump able to pass solid particles through its impeller and housing without breaking off any fins. Basic differences between standard water pump and trash pump involve materials of which pumps made and spacing their impeller fins. Fins on trash pump’s impeller spaced farther apart so debris can pass through without damage to pump.