How to Tear Down and Clean a DE Grid Filter

Why this matters

A DE filter that only ever gets backwashed is a filter whose grids are slowly caking with oils and old powder that backwashing never reaches. Starting pressure creeps up, run time stops buying clean water, and eventually a grid tears and blows powder into the pool on a Saturday afternoon. A full teardown once or twice a season resets the filter. It is also the only time anyone sees the grids, so it is where a torn grid or a cracked manifold gets caught before it becomes a callback. Backwash-only service stays in 'Filter Cleaning and Media Replacement'; this card is the teardown.

Safety first: pressure, startup and the powder

The tank is a pressure vessel, and the lid is what fails. A clamp band or lid released with the tank under pressure, or a pump started with the air relief closed after reassembly, is the condition under which lids separate and injure people. Every step that loosens the band happens with the pump off and locked out and the gauge reading zero with the relief open. Every restart happens with the relief open and nobody standing over the lid.

Lock out the pump before you open anything. Switch the heater off first and let the pump run a few minutes so the heat exchanger is not left hot and still. Then turn the pump off at its disconnect or breaker and lock and tag it so an automation schedule or a customer cannot start it while the tank is open, under 29 CFR 1910.147 for the stored energy of a pump starting against an open filter. Turn off any automation schedule as well, so the system does not try to start against a lock. The restore step is at the end.

DE powder is a respiratory hazard. Most pool-grade diatomaceous earth is flux-calcined, which converts part of it to crystalline silica. Dry powder becomes airborne when you open a bag, scoop it or pour it. Pour it as a slurry, keep your face out of the bag, and wear a respirator for dry handling under your shop's written respiratory program per 29 CFR 1910.134; the silica exposure itself falls under 29 CFR 1910.1053 unless the shop can show, in substance, that exposure stays below its action level under any foreseeable conditions. Spent DE coming off the grids is wet and much less of an airborne problem; keep it wet and do not let it dry and blow on the deck.

Hose water and the pad's electrics. Hose the grids away from the pump motor, the time clock and the automation panel. Spray into a motor or a junction box is how a GFCI trips or worse.

Start state

Bring: a garden hose with a fan nozzle (not a pressure washer), the filter's maker manual or label, silicone lubricant (never petroleum grease on o-rings), a replacement tank o-ring, a replacement grid of the right size if the filter is older, DE in the amount the filter label calls for, a clean bucket for the DE slurry, gloves and eye protection, and the respirator for the powder.

Read and record before you start: the arrival pressure and the recorded clean baseline from the equipment tag. 'Filter Cleaning and Media Replacement' sets the clean point at 8 to 10 psi above baseline; a teardown on schedule may come sooner.

Check the discharge rules. Spent DE and the water carrying it do not go to a storm drain. Many localities require it to settle in a separation tank or bag, and some allow the sanitary sewer through a cleanout while others bar DE from it; follow the local ordinance and the customer's setup.

   VERTICAL GRID DE FILTER, EXPLODED

          air relief valve (top of lid)
                 |
        +--------+---------+  <- tank lid
        |   air bleed tube |
   =====+==================+=====  <- clamp band over
        |   tank o-ring    |          lid-tank joint
        |  [  manifold  ]  |  <- grids hang from it
        |   | | | | | |    |
        |   |G|G|G|G|g|    |  G = full grid
        |   | | | | | |    |  g = short grid that
        |   | | | | | |    |      clears the inlet
        |  [  spreader  ]  |  <- bottom support plate
        |        |         |
        |    standpipe     |  <- manifold to outlet
        +--------+---------+
       inlet   outlet   drain plug

   flow: inlet -> tank -> through grid cloth
         -> manifold -> down standpipe -> outlet

The teardown

1. Heater off, run on, then pump off and locked out. As above. What breaks if skipped: the pump restarting on a timer against an open tank throws water and grids across the pad.

2. Open the air relief and watch the gauge go to zero. Leave the relief open for the whole job. A gauge that will not drop below a few psi is either stuck or reading pressure from a head of water above it; in both cases treat the tank as pressurized until the drain step proves it empty.

3. Close valves if the pad sits below water level, then drain the tank. Without closed valves, pool water keeps flooding the tank as you open it. Pull the drain plug, keep the plug and its o-ring together, and let the tank empty to wherever the local rule sends it.

4. Loosen the clamp band and lift the lid. Back the band off evenly. If the lid is stuck, work it gently at the seam; prying with a screwdriver nicks the sealing surface and creates the leak you will chase next month.

5. Note the orientation, then lift the grid assembly out by the manifold. Mark which way the manifold faces and where the short grid sits before you lift. Lift straight up so grids do not snag on the tank wall. Set it upright on a clean surface.

6. Separate the grids and hose each one, top to bottom. Remove the spreader and slide the grids out. Fan nozzle, top to bottom so dirt washes off rather than back in, both faces and into the seams. If the cloth stays gray or stiff after rinsing, the oils need a degreasing soak, and scale needs an acid soak after the degreaser, never before, per 'Filter Cleaning and Media Replacement'.

7. Inspect every grid and the hardware. Hold each grid to the light. Look for tears or pinholes, especially at the top shoulder where the grid meets the manifold, broken or crushed ribs, and worn spots where the cloth rubs. Check the manifold for cracks, the standpipe o-ring, the air bleed tube (a clogged bleed screen stops air leaving the tank), and the tank o-ring for flat spots or cuts. A torn grid is what blows DE into the pool after a recharge; replace it now, not next visit.

8. Reassemble in reverse. Grids into the spreader and manifold in the orientation you marked, short grid in its slot, assembly back down the standpipe so it seats fully. Clean and lightly lubricate the tank o-ring with silicone. Seat the lid and tighten the band evenly until the gap is uniform all round.

9. Restore: drain plug in, valves open, unlock, restart with the relief open and stand clear of the lid. This is the step where energy goes back in. Drain plug and its o-ring first, valves back to their run positions. Remove your lock and tag, restore power, and start the pump with the relief open and nobody's face or body over the lid. Purge until the relief spits solid water, then close it. Check the band seam, drain plug and lid for leaks under pressure. Read the bare-grid pressure.

10. Recharge with DE through the skimmer, in the amount on the filter label. Labels commonly call for around 1 lb per 10 sq ft of filter area, but the label governs. Mix the weighed powder into a bucket of water to a thin slurry (respirator on for the pour into the bucket), then pour it slowly into the skimmer with the pump running. Never add DE before the restart: on a bare, dry grid it clumps and does not coat evenly.

11. Log the clean starting pressure. Read the gauge after the DE has coated the grids, a few minutes in. This is the new baseline. Restore the heater and any automation schedule you turned off, and confirm the heater fires with the pump running.

Worked example: a 60 sq ft DE filter at mid-season

A 60 sq ft vertical grid filter on a 20,000 gal pool. Equipment tag shows a clean baseline of 14 psi from the spring teardown. Arrival: 23 psi, 9 psi over baseline, inside the 8 to 10 psi window. The last two visits were backwashes that brought it down only 3 psi each time and it climbed back within a week, which is the signature of grids caking past what backwashing reaches.

Teardown. Heater off, pump run three minutes, pump locked out at the disconnect, automation schedule paused. Relief open, gauge to zero. Pad sits above water level, so no valves to close. Tank drained to the separation bag the customer's setup uses.

Inspection. Seven full grids and one short grid. Six cloths rinse back to white. One full grid stays gray along the bottom and gets a degreasing soak and rinse, which brings it back. The short grid has a 1 in tear at its top shoulder, the classic wear point, so it is replaced from the truck. Tank o-ring is sound; cleaned and lubricated.

Restart. Relief open, lock removed, pump started from beside the tank, not over it. Solid water at the relief after about 20 seconds; relief closed, no leaks at the band. Bare-grid pressure 12 psi.

Recharge. The label calls for 6 lb for this 60 sq ft filter, which matches the 1 lb per 10 sq ft rule. 6 lb weighed, slurried in a bucket, poured into the skimmer. Pressure settles at 15 psi.

Judgment. 15 psi is 1 psi above the spring baseline of 14, inside the 2 psi return rule in 'Filter Cleaning and Media Replacement', so the grids are serviceable. 15 psi goes on the tag as the new baseline. Next clean is due at 23 to 25 psi. Heater fired and held for 15 minutes with no flow trip; automation schedule restored.

What changes the job

• DE in the pool after the recharge. A torn grid, a cracked manifold, a grid not seated in the manifold, or a broken standpipe o-ring. Tear down again; the sibling fault tree for powder blown back covers the order.
• Pressure will not return near baseline after a full clean. The grids are at end of life or the cloth is scaled; a set showing more than about 2 psi over its baseline after cleaning gets quoted for replacement.
• A filter with a bump handle rather than a backwash valve. Bumping knocks DE off the grids between teardowns; it does not replace one.
• A filter you have never opened. Read the maker's manual for the assembly before lifting anything; grid counts, manifold designs and band styles vary.

References

• See related: Filter Cleaning and Media Replacement (backwash-only service, pressure rules, soak order)
• 29 CFR 1910.147 (control of hazardous energy, for locking out the pump)
• 29 CFR 1910.134 (respiratory protection program) and 29 CFR 1910.1053 (respirable crystalline silica, general industry)
• Filter manufacturer's installation and operation manual and label (DE amount, assembly, o-ring service)