Flooded and suction head

Flooded suction and suction head refer to the position of the pump in relation to the fluid it is pumping:

Flooded suction

A flooded suction pump is designed to work by being gravity-fed the fluid that is to be pumped. This type of pump does not require a method of priming the fluid. There are numerous types of flooded suction pumps. A flood suction pump application is unlike a submersible pump application. In a flooded suction pump application, the pump and the pump motor are located outside of the fluid to be pumped. Whereas, in a submersible pump application the pump and the pump motor are located inside of the fluid that is to be pumped.

Advantages of Flooded Suction Pumps:

The flooded suction pump offers several major advantages over other types of pumps: Priming: They don’t have to be primed. They are automatically primed because the fluid they will be pumping is gravity fed directly into the pump, always keeping it primed. Efficiency: When a pump is submerged there is positive fluid pressure at the inlet of the pump. This condition can increase efficiency due to the less energy required to move fluid through the liquid path of the pump. Maintenance & Accessibility: When the pump is located outside of the fluid being pumped, the pump can be easily accessible for routine maintenance. A shut-off valve should be positioned before the inlet of the pump which will allow the fluid to the pump to be shut off, then, the pump can be easily removed from the application.

Disadvantages to contend with:

Potential to lose Prime: If the slurry mixture is too thick or viscous, it may not easily feed into the pump which can cause the pump to lose prime. Thus, the mixture needs maintain adequate fluidity to constantly feed the pump and prevent this from happening. Corrosion: Prolonged exposure to a liquid of any sort will lead to corrosion. Submersible pumps are often used to handle liquids that are corrosive and abrasive. Seals are especially prone to corrosion, which leads to leaks and damage to the motor. To counteract corrosion these pumps need to be made of corrosion-resistant material, which can make them more expensive than other types of pumps of the same capacity. Low level in feed may cause a coriolis (swirl) effect that may cause the pump to suck in air, instead of fluid. Wherever possible, flooded suction pumps should be inspected as often as possible. In this way, any necessary repairs can then be carried out to prolong the life of the pump.

Suction head

With a suction head the pump is above the fluid level.  This pumping arrangement is normally is the more problematic of the two arrangements.  The pump has to create a vacuum and maintain a vacuum in the suction side of the pump to work.

Failures of pumps with suction head:

Air leaking into pump through pipe joints and mechanical seals, destroying negative pressure to operate Block strainer Foot valve above water level Foot valve faulty impeller blocked Impeller not spinning fast enough Suction head to high Cavitation of pump