Flexible Rubber Connections for Drainbox Inline Water Level Controllers

Our 6-inch Inline Water Level Control Structures are designed to accept standard flexible rubber couplings suitable for PVC or single-wall plastic drain pipe on both the inlet and outlet sides.

The diameter of the inlet and outlet pipe stubs on our six-inch Drainbox products are made to match 6-inch Schedule 40 PVC pipe. 

Flexible rubber couplings fit over our aluminum outlet stubs and the mating PVC pipe. The couplings are tightened with band clamps to form a watertight seal.  These couplings are not rated for delivery water pressure but they are tested to 4.3 psi which equates to 10 feet of head pressure that might be encountered in a drainpipe application. 

Two commercial sources for these couplings are:

Fernco          1056-66

Bluefin          FRC600

Interestingly, there is not a standard rubber flex coupling available specifically for SDR 35.    Likewise, the manufacturers do not specifically caution against using these connectors on SDR 35.  They simply designate one diameter for “plastic or cast iron” pipe. The straight end of an SDR 35 pipe is smaller than a Schedule 40 pipe.   A flexible rubber connector fits loosely. It is common practice to tighten the clamp to cinch the coupling onto the straight end.  The outside diameter for a 6-inch SDR 35 bell mouth is slightly larger than a Schedule 40 pipe.  With slight persuasion, a flexible rubber coupling can be pushed onto the outside of the bell end of an SDR 35 pipe to achieve a tight seal.   While this is unconventional, it works well.

A plastic sewer pipe coupling on the straight end of an SDR 35 pipe could be used as a bushing to provide a better fit for a flexible rubber coupling.

For heights above 10 feet, use a strongback shielded coupling.     These have a metal reinforcement around the flexible rubber portion of the coupling to add strength.

Fernco          1056-66RC

Orienting the PVC pipe -- what is the correct direction for the bell mouth?

Manufacturers say that the direction of the bell mouth does not make a difference for water flow in normal situations – water will flow properly in either direction.   Common practice in drainage applications is to put the bell mouth on the “uphill side” of the pipe.  Our experience indicates it is not critical.