The ‘Dual Drain Test’ on hold down force
Ten years ago, the Pool Safety Council produced a video called “Dual Drain Test” concerning suction entrapment which is available for viewing on Youtube. This informative and relevant video illustrates the differences in Dynamic Hold Down Force when little more than pipe size is changed.
The purpose of the video is to show the effects of sump connection size and interconnecting pipe diameter on dynamic hold down force for a dual drain system when one sump is blocked and all flow is routed through the remaining open sump.
The test featured two identical drain systems with the exception of sump connection size and interconnecting pipe diameter.
Both dual drain systems are spaced 36 inches apart, when measured from sump center to sump center.
The tests were run at a constant flow rate of 63 gpm. One dual drain system features a 2-inch drain system, while the other is plumbed with 2 ½ inch pipes.
On each of the dual drain systems, one sump is left uncovered, while the other is covered with an ASME/ANSI A112.19.8 approved suction outlet in place.
A 15-pound rubber ducky is placed over the uncovered sump to test the dynamic hold down force for each of the two dual drain systems.
In the dual drain system featuring the 2-inch pipe size plumbing, the ducky becomes stuck to the drain, indicating that the dynamic hold down force is in excess of 15 pounds.
In the case of the dual drain system featuring 2 ½ inch pipe size plumbing, the same 15-pound duck does not become stuck to the drain, indicating that the hold down force is less than 15 pounds.
The same test is then run at 84 gpm, which is more typical of how newly constructed pools circulate.
Once again, the duck sticks to the drain in the 2-inch plumbed system, but floats free in the 2 1/2 -inch system.
The video clearly shows that the hold down forces are dramatically impacted by system plumbing. Sump Connector size and interconnecting pump diameter have a direct impact on the hold down force.
Conclusion: 2 ½-inch plumbing and larger help minimize the hold down forces.
Watchthevideohere:https://www. youtube.com/watch?v=KsBSJtzhEc& t=51s.