Drafting Tip #14 - Low Level Strainers
 
By President Mark Davis
February 2, 2017
 

While low level suction strainers were designed for use in dump tank operations, they can also be used in other situations when needed. A low level strainer can be used on a concrete boat ramp, a rocky bottom stream, or even in swimming pool. At our 2011 water supply drill in Dekalb County, Alabama, a 6-inch low level strainer was used at a pond because the pumper assigned to operate the tanker fill site only had a low level strainer. While not ideal, it did work okay and tankers were loaded in a reasonable time. A barrel or floating strainer was not available...thus, folks had to work with what they had.

The main problem with low level suction strainers is their flow - we simply do not know what they can produce unless we test them ahead of time. Odds are that on a 1250 gpm pumper a low level strainer will not support a 1250 gpm flow and may not support a 1,000 gpm flow! That being said, It is best to flow test your low level strainer so that you know its flow limit. This can be accomplished during the annual pump test on your pumper. Also...for maximum flow using a single suction inlet on a midship pump...use one of the main suction inlets (sides)...not a front suction inlet.
 
This 1,250 gpm pumper carried 5-inch LDH but had no high-flow discharge. No problem, two smaller lines were used to feed the single, 5-inch line which supplied the tanker loading station.
This 1,250 gpm pumper carried 5-inch LDH but had no high-flow discharge. No problem, two smaller lines were used to feed the single, 5-inch line which supplied the tanker loading station.
The goal was to load tankers at 1,000 gpm out on the "hard" road. The LDH allowed the 1250 gpm pumper to maximize its ability and not fight the friction loss in much smaller hose.
The goal was to load tankers at 1,000 gpm out on the "hard" road. The LDH allowed the 1250 gpm pumper to maximize its ability and not fight the friction loss in much smaller hose.
 
The low level strainer was supported by a folding ladder. A length of rope was used to secure the strainer and to allow the crew to adjust the location if needed. Best practice has a suction strainer always equipped with a piece of rope or webbing.
The low level strainer was supported by a folding ladder. A length of rope was used to secure the strainer and to allow the crew to adjust the location if needed. Best practice has a suction strainer always equipped with a piece of rope or webbing.
The crew came up short on suction hose, but no problems were encountered with a vortex.
The crew came up short on suction hose, but no problems were encountered with a vortex.