Desander and desilter suction & discharge pits

Desander suction pit

The suction pit for the desander is vacuum degasser discharge pit, usually. The desander, as well as the desilter, needs to be downstream of the degasser operation. If the hydrocyclone suction is upstream of the degasser operation and gas is present in the mud, the efficiency of the centrifugal pump will be reduced, or the pump will become gas locked and simply not pump any mud. Additionally, induced cavitation can occur and cause premature wear to the centrifugal pump. This wear can be rapid and severe.
 

Desander discharge pit

The desander discharge (cone overs) should flow into the next pit downstream, and a low equalizer between these tanks should be opened This allows backflow through the equalizer when the cone manifold is processing a greater volume than is entering the tank (recommended) This ensures that all of the drilling fluid is processed through the desander manifold.
Desander operation is typically recommended only for unweighted drilling fluids. If operated with weighted drilling fluid, the desander wil discard a lot of drilling fluid away, including a lot of weight material.
 

Desilter Suction and Discharge Pits (Mud Cleaner/Conditioner)

The desilter suction pit is the desander discharge pit. The desilter will remove smaller particles than the desander, so its operation is down- stream of the desander. Setup and operation of desilters are the same as with desanders. The manifold discharge is downstream of the suction with a low equalizer between the two tanks. It is recommended that the desilter process more volume than the rig is pumping so that there is a backflow through the equalizer, ensuring that all of the drilling fluid is processed.
 
If drilling fluid is being pumped through mud guns from the suction compartment downstream, this fluid must also be processed through the hydrocyclones. For weighted drilling fluids, the underflow of the desilter cones is processed by a shaker. Ideally this shaker will have screens installed that allow the weight material to pass through while rejecting any drilled solids larger than the weight material.