Abstract: A strainer system having two separate strainers positioned in parallel, where one strainer can be cleaned while still permitting normal flow through the other strainer. The system flow circuit is arranged so that a high pressure backwashing flow can be applied to one strainer while the other strainer is providing its normal straining function. The backwashed strainer is then isolated by valves so that its access flange can be removed and the particulate buildup within the valve plug cleaned out. The strainer is then returned to service following the replacement of the access flange. In this manner, it is possible to alternate between the two strainers so that continuous flow can be maintained to the hydraulic choke located downstream of the strainer system.

Abstract: The invention contemplates a strainer based upon a four-way, two-position rotary cylindrical plug valve having a hollow plug. The normal entry port for the sealing plug of the plug valve is a circular radial hole passing from the exterior of the plug into the interior cavity of the plug. The normal exit port for the sealing plug is a regular array of small holes across from and coaxial with the normal entry hole. The ports for the valve body are in two pairs positioned at 90° from each other, with the axes of the ports lying in the same transverse plane as the ports of the valve plug.