Generally, with the Defender filter it is possible to provide a catch basin adjacent to the filter to accept the backwash flow via gravity. This drain can generally handle a reasonable capacity appropriate for draining of the pool. The Defender simply drains (without restriction) to this basin.
In other cases, the Defender drains to a sump with a lift pump. In these instances, it may be necessary to store water or restrict the outflow from the Defender filter so that the capacity of the lift pump is not exceeded. This scenario becomes complicated because the filter drain rate is highest when the filter is full and reduces as the filter drains. Neptune Benson has said that if the Defender outflow is restricted, the tank may require an additional fill-bump-drain to get the elements clean. If possible, the project manager should design the basin such that the flow from the Defender does not require significant restriction. Nemato can accommodate these situations by backwashing under pressure at 08. GPM/SF.
Unlike a sand filter where the backwash flow rate is known and constant, a Defender is gravity draining where the flow is greatest with a full tank and gradually slows down as the tank empties. The drain can be throttled to regulate flow, but the most efficient drain of the media is with the valve wide open. The optimum size of the waste pit should be twice the size of the Defender tank volume, thereby causing no concerns if the waste piping was clogged. However, many facilities do not have the means to build up a large sump and with renovations, the project manager may be stuck with an existing sump. Neptune-Benson has used a flow program and modeled the Defender draining. The maximum flow rate calculated was 300 GPM. Filtrex specifies 500 GPM waste handling capacity.
PM should ensure that all regenerative media systems are provided with a water separator that includes an automatic drain (e.g. diaphragm) rather than one that has to be drained manually. At UNC-Wilmington, the Filtrex regenerative filters were provided with a small manual water separator. The air compressor was cycling on a normal frequency and the water separator was producing about 8 oz of water per hour. The owner had to drain the separator manually multiple times per day. If this wasn’t performed regularly, media was causing a valve failure and media was blown back to the pool on a few occasions. The pneumatic solenoid on the side of the filter would get water in it. When it accumulated, it caused the pneumatic pre-coat valves to not perform properly.
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