An Apollo backflow repair kit renews seals and check parts, then a certified test confirms safe operation.
A backflow preventer sits between your water supply and anything that could push dirty water backward. When the internal rubber and moving parts wear out, you may see dripping from the relief port, slow weeping at the bonnets, or a test failure during an annual inspection.
A repair kit lets you renew the wear parts without swapping the whole assembly. The trick is matching the kit to your exact Apollo model and size, then rebuilding with clean parts and the right torque so the body seals without damage.
What A Repair Kit Actually Replaces
Most Apollo kits center on three groups of parts. Each group solves a different failure pattern, so it helps to name what you’re chasing before you open the bonnet.
- Check rubber parts — Disc, seat disc, and related O-rings that let each check valve seal tight.
- Check assemblies — The full check module or poppet group when springs, stems, or holders are worn or scored.
- Relief valve parts — Diaphragm and O-rings on RPZ models that control the relief opening and reseal after a dump.
If your device is an RPZ, a steady drip from the relief port often points to worn check rubber, debris on a sealing edge, or a relief diaphragm that no longer seats clean. On a double check, you’re more likely to see a test failure with no visible leak.
Freeze damage is different. A cracked body, split bonnet, or bulged casting is not a “kit job.” In that case the safe move is replacement of the assembly and a new test.
Apollo Backflow Preventer Repair Kit Choices By Model And Size
Start with the data plate on the body. You’re looking for the series name, the size, and whether it is lead-free. Apollo models often have close cousins, and the internal kits can differ even when the body looks similar.
How To Identify Your Exact Unit
- Read the model marking — Look for names like RP4A, RPLF4A, DC4A, DCLF4A, or 40-200 series markings on larger units.
- Confirm the nominal size — Measure the connection size or read the stamped size on the body.
- Check for “LF” — Lead-free versions often use the same kit family, but verify with the kit listing for your exact series.
- Match the kit type — Decide whether you need rubber-only, check assemblies, relief valve parts, or a full internal kit.
Retail listings for Apollo kits usually group them by series and size, then break them into “rubber” kits and “complete internal” kits. A rubber kit is the lowest-cost refresh when the metal parts still look smooth. A complete internal kit costs more because it can contain full first and second check assemblies plus multiple O-rings and relief valve parts on RPZ models.
| Kit Category | What You Swap | Best Fit For |
|---|---|---|
| Check rubber kit | Disc and sealing O-rings for one or both checks | Seepage, dirty seal line, routine rebuild |
| Total rubber kit | All O-rings and discs for checks and relief parts | RPZ drip after winter, dry rubber, aging seals |
| Complete internal kit | Check assemblies plus multiple O-rings and relief pieces | Repeated failures, worn springs, scored holders |
The table is a quick sorter, not a substitute for a model match. Many suppliers list part numbers like 4A-007-10 for complete RP4A internals, or rubber kits that state they fit RP4A and RPLF4A in a given size. Use that fit statement as your anchor, not just the photo.
Order Mistakes That Waste Money
Wrong-kit orders usually come from a size guess or a near-match series. Match series letters, then size, then kit type. If a listing doesn’t name your size, skip it.
- Mixing series — RP4A, DC4A, and 4S internals differ.
- Missing size breaks — 1/2″, 3/4″, and 1″ kits are often different.
- Choosing rubber only — If springs or holders are worn, swap the full check module.
Repairing An Apollo Backflow Preventer With The Right Kit
Backflow devices protect drinking water, so treat the rebuild like a clean-room job. Wash your hands, work on a clean surface, and keep grit out of the body. If you’re not allowed to service the device in your area, hire a licensed plumber and schedule a certified tester for the final test.
Prep That Saves You From Rework
- Shut off water and relieve pressure — Close upstream and downstream shutoffs, then open test cocks to bleed pressure, and keep a towel under the body.
- Photograph the layout — Snap the check modules, spring orientation, and bonnet stack before parts move.
- Lay parts in order — Use a tray with left-to-right placement so first check and second check parts do not mix.
- Clean the body gently — Wipe with a lint-free cloth; avoid scratching sealing surfaces.
Keep a clean bucket nearby for old parts, so nothing rolls into dirt or grass.
Opening The Bonnets Without Damage
Loosen bolts evenly in a star pattern, then lift the bonnet straight up. If it sticks, tap the bonnet edge lightly with a rubber mallet. Do not pry between machined faces. A gouge on the sealing land can create a leak that no O-ring will stop.
Once the bonnet is off, remove the old O-ring and inspect the groove. If you see scale, wipe it out. If you see deep corrosion pitting, plan on extra cleaning time and a careful reseal.
Replacing Check Rubber Or Full Check Modules
With a rubber kit, you’ll pull the disc and the sealing O-rings, then install the new parts from the same pocket of the kit. With a full check assembly kit, you swap the module as a unit. Either way, keep the first check parts with the first check location and the second check parts with the second check location.
- Inspect the seating edge — Look for cuts, sand, or mineral crust where the disc meets the seat.
- Rinse debris away — Flush with clean water, then wipe dry so grit does not re-seat.
- Lubricate O-rings lightly — Use a potable-water-rated silicone grease in a thin film.
- Seat parts square — Press O-rings into grooves without twisting, then reinstall the module straight down.
Do not over-lube. Grease can trap grit, and a thick smear can pinch an O-ring during assembly.
Before you close up, confirm the flow arrow on the body and the direction marks on the check modules, if present. A check installed backward may move, yet it will not seal the way the test expects.
Relief Valve Repairs On Apollo RPZ Bodies
If your series is RP4A or RPLF4A, the relief valve is the “dump” path that opens when the zone pressure drops or when backpressure occurs. When the diaphragm or related O-rings age, you can see a steady drip that does not stop after the checks are renewed.
Signs The Relief Parts Need Attention
- Drip that won’t clear — Water keeps leaving the relief even after the line pressure is stable.
- Dump during normal flow — Relief opens while sprinklers or fixtures run with no obvious pressure swing.
- Test failure tied to zone pressure — A tester reports unstable zone readings that point to relief sealing.
Many complete internal kits for RPZ bodies list relief valve parts like the diaphragm, seat O-rings, sensing passage O-rings, and a relief module. That package can solve a leak that survives a check rubber rebuild.
Clean The Sensing Passages
On some bodies, scale builds in small passages that feed the relief zone. A kit will not fix a blocked passage. Use a soft brush and clean water, then blow through the port with low-pressure air if your procedures allow it. Keep debris out of the body.
After Reassembly Leak Checks And Required Testing
Once the new parts are in, reinstall the bonnets with the new bonnet O-rings. Tighten bolts evenly in a star pattern, then bring each bolt to the manufacturer’s torque spec if you have it. Uneven bolt load is a common cause of bonnet seepage.
Pressurize slowly. Crack the upstream shutoff, let the body fill, then open fully. Watch the bonnets and the relief port. A quick wetness at first can be trapped water. A steady bead means something is pinched or the sealing land has debris.
Also cycle each test cock. Open it for a second, then close it. A gritty feel can mean scale inside the cock, and that can create a drip that looks like a body leak.
Field Test Steps You Should Not Skip
Backflow preventers are normally required to pass a certified test after service. That test checks the first check, second check, and relief set points on RPZ units. In many areas, only certified testers can file the result with the water authority.
- Schedule the test right away — Don’t put the device back in service without a pass on record.
- Keep the kit packaging — Part numbers help if the tester sees a repeat pattern and you need to track what was swapped.
- Note your symptoms and fix — Write down “relief drip,” “bonnet seep,” or “failed first check” plus the parts replaced.
If the device fails again after a rebuild, the cause is often body damage, a missed piece of debris, or a mismatch between kit and series. At that point, swapping the full check assemblies and relief module may be the next step, or a full replacement may be the safer call.
Buying And Storing The Right Kit For Next Time
Once you’ve matched the model and size, save that info. The next rebuild goes faster when you already know the kit family, and it reduces the chance of ordering a near-match that does not seal.
Smart Buying Habits
- Match by series first — Order based on the exact series marking, then confirm size.
- Pick rubber or complete based on wear — Smooth metal seats often do fine with rubber parts; rough wear calls for assemblies.
- Buy spares before seasonal start-up — Irrigation systems see many rebuilds in spring, and stock can dip.
Store unused rubber parts in a sealed bag out of sun and heat. Rubber hardens with time, so don’t keep spares for years in a hot shed. If you do keep a spare apollo backflow preventer repair kit on hand, rotate it by using the oldest kit first.
Also watch your install location. If the unit is in a freeze zone, add a drain-down plan or insulation approved for the device location. Freeze cracks turn a simple rebuild into a replacement job.
When you’re ready to order again, repeat the match steps and verify the fit notes. The phrase “apollo backflow preventer repair kit” gets you close in search, yet the exact kit is still decided by series and size.