Hot Tub Filter Components page 2

You will normally find an air relief valve mounted on a yoke or T fitting along with the pressure gauge. This is simply a threaded plug that, when loosened, allows air to escape from the filter. Purging the air is important to proper filtration, because the air can displace water, essentially reducing the filter area of the sand, DE, or cartridge medium. When a circulation system first starts up, particularly after cleaning or if the pump lost prime, there is a lot of air present in the filter. If the air isn't purged, the filter may be operating only at one-half its capacity.

Figure 4-1 shows an inside view of a cartridge filter. The area above the cartridge is called the freeboard. This empty area is present above the filtration media of all filters. Air in this area is quite acceptable, since there is no filtration medium in the freeboard. Thus, it is important to let the air out of the filter at least once each week. Again, some air is normal, so don't be obsessive about this. Just be sure that the filtration medium itself is covered with water in the tank, not air.

Backwash Valves

As noted previously, backwashing is a method of cleaning a DE or sand filter (cartridge filters do not backwash) by running water backward through the filter, flushing the dirt out to a waste drain line or sewer line. There are two types of backwash valve—the piston and the rotary (with the multiport valve being a variation of the rotary valve). Since few filters today use the piston backwash valve, we will focus our attention on the more common, rotary type. Some filters use a rotary backwash valve like the one in Fig. 4-4A. Changing the direction of water flow is accomplished by rotating the interior rotor. A rotor gasket seal or 0-rings keep water from leaking into the wrong chamber.

Other filters use top- or side-mounted backwash valves (Fig. 4-6), while DE filters typically mount the valve underneath the tank. In any of these designs, a handle allows you to rotate the interior rotor to align with the openings of the valve body as desired.