In pumping installations whose scheme coincides with the one indicated in the attached diagram, an additional system is necessary to prevent the sanitary pump from being descending. Some of these systems are listed below:

1. You can build a hole in the upper part of the pump casing and pour water on it so that the pump when turned on is full of water and can pump correctly. It is not a very efficient system.
2. You can use a valve foot (check valve). It allows the passage of the liquid to the pump but prevents its return to the tank once the pump has been turned off, which prevents the discharge of the discharge pipe. It can present problems when the fluid has dirt that is deposited in the seat of the valve decreasing its tightness; on the other hand it supposes a loss of load more or less important in the impulsion pipeline which increases the risk of cavitation occurring in the bomb.
3. Use of a vacuum sanitary pump. The vacuum pump is a positive displacement pump that draws the air from the discharge line and causes the fluid to reach the centrifugal pump and thus be primed.
4. Another possibility is to install the pump under load, i.e. below the level of the liquid, although this arrangement is not always possible, unless it is installed submerged, so the pump must be special.