AODD Pump Parts: Wet End vs Air End
Most AODD pump parts orders fail for one reason: the buyer treats the pump as one assembly. An air-operated double-diaphragm pump is two machines sharing a shaft. The wet end (liquid chambers, diaphragms, valve balls, seats) sees the process fluid. The air end (air valve, pilot sleeve, gaskets, glyd-rings) sees compressed air. A diaphragm pump repair kit that rebuilds the wrong side leaves the leak you came to fix.
We stock OEM kits and aftermarket diaphragm pump parts across Wilden, Yamada, ARO, All-Flo, and Nomad. This guide is the order we use on the counter: identify wet end vs air end, read the model code, pick the elastomer, then decide OEM vs aftermarket. If you only have a leaking nameplate, send a photo and we will cross-reference it.
Split the Pump
Product out the exhaust is a wet-end failure. Slow cycling, icing, or air blow-by is an air-end failure. Order the kit that matches the failure, not a generic rebuild.
Read the Model Code
Size, ADS family, wetted material, and elastomer all live in the nameplate string. A P4 aluminum Wil-Flex pump does not take a P400 plastic PTFE wet kit.
Match the Elastomer
Buna-N, EPDM, PTFE, and Santoprene (Wil-Flex) are not interchangeable by price. Chemical class and temperature set the material before you shop SKUs.
Wet end (process side)
Diaphragms, valve balls, valve seats, and the gaskets or o-rings that seal the liquid path. This is what you replace when the pump passes fluid out the muffler, loses prime, or starts passing solids past the checks.
Wilden Wet Kit definition: WIL-19100-F-04 (03-2021).
Air end (ADS side)
Air valve spool, pilot sleeve, air-valve and center-block gaskets, muffler-plate gasket, glyd-rings, retaining rings, shaft bushings. This is what you replace when the pump stalls, chatters, or dumps air without shifting.
Wilden Air Kit definition: WIL-19100-F-04. T-Series Air Kits still ship a complete air valve assembly.
Bleed the air line before you crack a cover
Wilden P4 EOM (WIL-10183-E-04) and the Nomad NPF manuals use the same lockout: disconnect the air line, bleed residual pressure, disconnect suction and discharge, then drain the pump into a suitable container. Do not apply air to the exhaust port. Do not exceed the published air-supply limit for that brand (Wilden P4: 125 psig; ARO PX15X: 120 psig).
How to Read a Diaphragm Pump Model Code
A Wilden repair kit is coded to the pump, not to the duty. Start on the nameplate, not on a memory of "the 1-1/2 inch aluminum one." Wilden writes the configuration as a slash-separated string. We will walk P4/AAAPP/PUS/NE/NE (catalog SKU 04-11120, clamped metal Pro-Flo P4) using Section 2 of the P4 EOM.
P4 / WETTED + OUTER + AIR CHAMBER + CENTER + AIR VALVE / DIAPHRAGM / BALL / SEAT / SPECIALTY Â |Â Example: P4 / A A A P P / PUS / NE / NE
P4
Means: Pro-Flo ADS, 38 mm (1-1/2 in) clamped metal family
This pump: Not P400 plastic, not PS4 SHIFT, not PX4
A (wetted)
Means: Aluminum liquid path
This pump: Also S = stainless, W = ductile iron
A (outer piston)
Means: Aluminum outer piston (Z = no outer piston / IPD)
This pump: Changes the wet kit if you run Chem-Fuse or Pure-Fuse
A / P / P
Means: Aluminum air chambers, polypropylene center block, polypropylene air valve
This pump: Sets which Air Kit (metal vs plastic air valve) you order
PUS
Means: Polyurethane diaphragms (clear)
This pump: Wet kit must be PUS, not NES or TSU
NE / NE
Means: Neoprene valve balls and neoprene seat o-rings
This pump: Balls and seats can differ from the diaphragm. Read all three.
Source: Wilden P4 Clamped Metal EOM, WIL-10183-E-04, Section 2 (material codes) plus catalog row 04-11120.
Wilden kit codes use a different grammar
The 2021 Wilden parts-kit program (WIL-19100-F-04) replaced the old Elastomer Kit with the Wet Kit and the old ADS Kit with the Air Kit, cutting duplicate and unneeded parts. Wet Kits and Air Kits are ordered separately, and each kit covers a family of pumps.
Wet Kit code
KIT, WET, AA/B/C/DDD
- AA size: 0.5, 1, 1.5, 2, 3
- B configuration: O original, A advanced, D FIT, C combo, H high pressure, S Stallion, F Brahma flap
- C pump material: M all metal, A aluminum only, S SS/Alloy C only, P all plastic
- DDD elastomer: BNS Buna-N, EPS EPDM, NES neoprene, WFS Wil-Flex, TSU PTFE/Saniflex backup, and the rest of the published list
Air Kit code
KIT, AIR, AA/BB/C/D/E/F
- AA ADS: T Turbo-Flo, P Pro-Flo, PX Pro-Flo X, PS Pro-Flo SHIFT, H high pressure
- BB size: 0.5 through 4
- C / D configuration and pump material (combo configuration covers Original, Advanced, and Advanced FIT; combo pump material covers metal and plastic)
- E air-valve material: M metal, P plastic, B brass (Turbo-Flo), R anodized aluminum
Worked kit examples from our catalog (both live on Wilden repair kits):
- 04-9804-51 is a 1.5 in combo metal Wet Kit, model-number 1.5 in/C/M/NES (neoprene).
- 04-9993-99-320 is a Pro-Flo SHIFT Air Kit for 1.5-2 in combo metal pumps with metal air valves (PS/1.5 in-2 in/C/M/M/S).
- Combo (C) wet kits cover Original and Advanced only; an Advanced FIT wet end needs the D configuration. Combo (C) air kits cover Original, Advanced, and Advanced FIT. Source: WIL-19100-F-04 footnotes.
Wet-End Kit vs Air-End Kit: What You Actually Get
Do not assume "repair kit" means every wear part. Wilden's 2021 kit refresh cut duplicate ADS pieces out of the wet-side box. ARO splits the same idea as a fluid-section kit vs an air-section kit. If you order one box and expect both sides, you will be short on the floor.
Diaphragms (2)
Wet: Yes
Air: No
ARO: Fluid section kit 637375-XXX (with seats) or 637375-XX (no seats)
Valve balls (4)
Wet: Yes
Air: No
ARO: In the fluid section kit
Valve seats / seat o-rings
Wet: Yes (seats or o-rings as required)
Air: No
ARO: Only in 637375-XXX (with seats). 637375-XX omits seats.
Liquid-path gaskets / o-rings
Wet: Yes, if the pump uses them
Air: No
ARO: Fluid section kit. IOM note: that kit also packs the diaphragm-rod U-cups and an air-motor o-ring; replace them while you are in the pump.
Air valve spool
Complete air valve assembly
Wet: No
Air: No, except T-Series (Turbo-Flo) Air Kits
ARO: Major air valve assembly 637390-X, sold separately from 637389
Pilot sleeve / glyd-rings / bushings
Wet: No
Air: Yes (see 04-9993-99-320 packing list)
ARO: Air section kit 637389
Muffler plate
Wet: No
Air: No (gasket only; plate removed from the new Air Kit)
ARO: Not in the air section kit as a plate. Confirm on the IOM exploded view.
Wilden columns: WIL-19100-F-04 plus catalog specs on 04-9804-51 and 04-9993-99-320. ARO column: PX15X IOM REV AF (12-6-24), Service Kits block, and live SKUs 637375-AA / 637389 / 637390-1.
The 1.5 in neoprene combo wet kit 04-9804-51 is a useful packing-list check: primary diaphragms (2), diaphragm installation tools (2), valve balls (4), valve seats (4). The SHIFT air kit 04-9993-99-320 packs an air valve spool, pilot sleeve, air-valve gasket, two center-block gaskets, muffler-plate gasket, spool and end-cap o-rings, glyd-rings, extra o-rings, retaining rings, shaft bushings, and a grease packet. That is an air-end rebuild, not a wet-end rebuild.
If the muffler is spitting product, do not start with an air valve repair kit. Fluid in the exhaust is a ruptured diaphragm or a loose outer piston (Wilden P4 EOM troubleshooting; Nomad NPF manuals use the same symptom). Order the Wet Kit for that size / configuration / elastomer. Add the Air Kit only if the pump was also stalling or icing before the rupture.
Elastomer Selection: Buna-N, EPDM, PTFE, Santoprene
The cheapest diaphragm pump repair kit is the one whose elastomer matches the fluid. Wilden groups diaphragms into rubber, TPE, and PTFE (WIL-19180-C-12). Temperature limits below are mechanical-stress limits only. The P4 EOM and the Nomad NPF manuals both warn that a chemical can cut those ceilings sharply. When housing and elastomer disagree, the weaker part wins: FKM is published to 350 F, but a polypropylene center section on the same pump is published to 175 F.
Buna-N (Nitrile, BNS)
Temp: 10 F to 180 F
Use: Petroleum and oil-based fluids
Skip: Ketones, strong acids, ozone-heavy outdoor duty
EPDM (EPS / Nordel)
Temp: -60 F to 280 F
Use: Dilute acids and caustics, hot water, cold weather
Skip: Petroleum oils and most hydrocarbons
Neoprene (NES)
Temp: 0 F to 200 F
Use: Water, seawater, mild water-based slurries (general service)
Skip: Aggressive aromatics and strong solvents
Wil-Flex / Santoprene (WFS, TPE)
Temp: -40 F to 225 F (traditional shape)
Use: Acids and caustics (NaOH, sulfuric, hydrochloric), abrasion
Skip: Aromatics and chlorinated hydrocarbons (use PTFE or FKM)
PTFE (TEU / TSU / TSS / TWS)
Temp: 40 F to 220 F (Wilden)
Use: Aggressive chemicals: aromatics, chlorinated solvents, strong acids and caustics, ketones, aldehydes, acetates
Skip: Abrasive slurries if you can use a TPE instead. Reduced-stroke PTFE also cuts displacement.
FKM (VTS / Viton)
Temp: -40 F to 350 F
Use: Hot hydrocarbons, aromatics, chlorinated solvents
Skip: Ketones and amines. Confirm the housing temp, not just the diaphragm.
Temps dual-sourced: Wilden Diaphragms WIL-19180-C-12 table plus Wilden P4 EOM WIL-10183-E-04 Section 1, and Nomad NPF07/NPF25 manuals (Buna-N, EPDM, Neoprene, 350 F Viton note). ARO PX15X IOM publishes PTFE to 225 F (single-source ARO figure; we keep Wilden's 220 F in the Wilden column). Wil-Flex Chem-Fuse/EZ-Install shapes are published to -58 F to 266 F on the same Wilden diaphragm table; traditional Wil-Flex stays -40 F to 225 F.
PTFE backup diaphragms are not optional trivia
A PTFE wet kit is a two-layer stack: the PTFE face plus a rubber or TPE backup (neoprene, EPDM, Saniflex, or Wil-Flex). Wilden kit codes encode the backup (TEU, TNU, TSU, TSS, TWS). Ordering "PTFE" without the backup letter is how you get a kit that will not torque onto the shaft. Full-stroke PTFE (TSS/TWS) uses the same shaft and pistons as rubber/TPE and is the reason a P4 full-stroke PTFE-fitted pump is published at 87.2 GPM vs 78 GPM reduced-stroke PTFE and 76 GPM rubber-fitted (P4 EOM Section 5). Air-supply ceiling on that same EOM is 125 psig for every P4 fit.
What we need to pick the elastomer
Have these ready before you ask for a Wilden repair kit or an ARO fluid-section kit.
OEM vs Aftermarket: Nomad-for-Wilden Honesty
Aftermarket diaphragm pump parts are real, and they are not automatically a downgrade. They are also not a free substitution. The honest split is: OEM when the air valve, warranty, or a current-generation ADS is on the line; aftermarket when the interchange is documented and you are replacing wet-end wear parts on a known pump.
Buy OEM when
The pump is still in the Wilden warranty window (P4 EOM: 5 years from install or 6 years from manufacture, whichever comes first). You are on Pro-Flo SHIFT, Advanced FIT, Saniflo, Brahma, or any ADS the aftermarket line has not published a current kit for. You need the factory Wet Kit / Air Kit packing list to match a nameplate without guesswork.
Consider aftermarket when
The interchange is printed in current manufacturer literature, the nameplate is readable, and you are replacing diaphragms, balls, and seats on a clamped Original or similar generation. Price only wins after those three are true.
What current Nomad literature actually supports
Nomad is a separate aftermarket brand from JDA Global, not a Wilden product line. Distributor listings describe the NPF PWR-FLO pumps as Wilden-style, and the current NPF25 metallic operation manual uses N-prefix part numbers that mirror Wilden numbering: N 01-2010-20 is the NPF25 air valve assembly, and 01-2010-20 is a live Wilden spare-part SKU in our catalog. The NPF07 and NPF25 manuals publish the same mechanical temperature band we use for Wilden rubber (Buna-N 10-180 F, EPDM -60-280 F, Neoprene 0-200 F) and the same 125 psig air-supply ceiling. That is current manufacturer literature, not a blog rumor.
What we will not pretend is on this site
The legacy Pump Catalog posts pointed at /nomad/wilden-replacement-parts/ and /nomad/wilden-replacement-kits/. Those paths are not in the live pump-catalog category tree. Today, Nomad aftermarket categories we can link are Warren Rupp parts, Warren Rupp kits, Versamatic, Graco, Garlock, Blagdon, and Dorr-Oliver. We also stock Nomad's own AODD pumps.
If you need a Nomad N-prefix stand-in for a Wilden 04- or 08- wear part, send the Wilden SKU and the nameplate. We will check current Nomad literature and available stock before we call it interchangeable. We will not publish a dead Wilden-compatible Nomad category just because the old site had one.
For Graco, Sandpiper, Versa-Matic, DEPA, and All-Flo aftermarket (not Wilden, and not ARO: our ARO aisle is OEM only), the live brand is ThinQk. That is a different interchange family. Do not mix a ThinQk Sandpiper kit onto a Wilden P4, and do not mix a Nomad Warren Rupp kit onto a Wilden air valve.
Air valves are the aftermarket risk
Wet-end elastomers are dimensionally simple: a diaphragm either seats on the piston and bead or it does not. Air-valve spools, pilot sleeves, and glyd-rings are the parts that stall a pump when the bore is off by a few thousandths. If you are buying an air valve repair kit for a SHIFT or Pro-Flo X pump, start with the OEM Air Kit (04-9993-99-320 for 1.5-2 in metal SHIFT) unless current Nomad literature lists that exact ADS.
Where to Shop AODD Repair Kits on This Site
Every path below is a live pump-catalog category (dev DB, 2026-08-30). Brand hubs: Wilden, Nomad, Yamada, ARO, All-Flo. Type hub: diaphragm pumps.
771 SKUs in Repair Kits - Air End / Wet End Spare Parts, including 04-9804-51 (wet) and 04-9993-99-320 (air). Loose diaphragms and piece parts live in Diaphragms and spare repair parts (2,166 SKUs).
Watch for: Match ADS family (P vs PS vs PX vs T) before you match size. A P4 Air Kit is not a PS4 Air Kit.
432 kit SKUs (example: K25-PT). Piece parts are under Yamada repair parts (2,364 SKUs). Yamada kit codes are series-based (K25, KG15), not Wilden slash-codes.
Watch for: A Yamada kit will not service a Wilden pump of the same port size.
9,200 SKUs. PX15X metallic IOM calls 637375-AA the fluid-section kit family and 637389 the air-section kit. Major air valve is 637390-X.
Watch for: ARO PX15X max air inlet is 120 psig (not Wilden's 125). Max published flow on that IOM is 123 GPM flooded inlet.
1,142 SKUs under the All-Flo hub, kits and piece parts alike (example kit SKU: 78000-00). Start at the All-Flo brand page if you are not sure you have an All-Flo, not an ARO.
Watch for: All-Flo aftermarket piece parts also exist under ThinQk All-Flo (10 SKUs). Confirm which brand is on the nameplate.
1,603 SKUs. Aftermarket on this site is Warren Rupp, Versamatic, Graco, Garlock, Blagdon, and Dorr-Oliver. Nomad's own pumps are under Nomad diaphragm pumps.
Watch for: No live Nomad-for-Wilden category. See the OEM vs aftermarket section.
7,449 SKUs. Use this for aftermarket diaphragm pump parts on Graco, Sandpiper, Versa-Matic, DEPA, Verder-Air, Blagdon, Tapflo, Johnson, Flux, and All-Flo. It is not a Wilden parts aisle, and it does not carry ARO-compatible parts; for ARO, stay OEM.
Common Kit-Ordering Mistakes
Ordering an air valve repair kit because the muffler is wet
Product out the exhaust is a diaphragm or outer-piston problem (P4 EOM and Nomad NPF troubleshooting). An air-end kit will not stop a ruptured diaphragm. Order the Wet Kit first.
Matching port size and ignoring ADS family
A 1.5 in Wilden is P4, P400, P420/P430, PS4, or PS420/PS430 depending on clamped vs bolted and Pro-Flo vs SHIFT. The Air Kit code starts with the ADS letter (P, PX, PS, T). Size alone is not a kit number.
Swapping Buna-N onto an EPDM chemical duty because the box was cheaper
Buna-N is the oil diaphragm (10-180 F). EPDM is the dilute-acid / cold-weather diaphragm (-60-280 F). They share a pump family, not a fluid class. Wilden Diaphragms WIL-19180-C-12 is explicit on both.
Ordering PTFE without the backup letter
TEU, TNU, TSU, TSS, and TWS are different stacks. Full-stroke PTFE also changes flow (P4: 87.2 GPM vs 78 GPM reduced-stroke). If the nameplate says TSU, a generic "PTFE kit" is not a match.
Assuming the old Nomad-for-Wilden URL still exists
It does not, on this catalog. OEM Wilden kits are at air-kits-wet-end-repair-parts. Nomad aftermarket here is other OEM brands. Ask us to cross a specific N-prefix SKU against current Nomad literature.
Frequently Asked Questions
What AODD pump parts do I need for a leaking muffler?
A wet-end kit: diaphragms, valve balls, and seats (plus liquid-path gaskets if the pump uses them). Fluid in the exhaust means the diaphragm or outer piston has failed, not the air valve. On Wilden, start in Repair Kits - Air End / Wet End with the size / configuration / elastomer from the nameplate.
What is in a Wilden repair kit?
Two different boxes. A Wet Kit (WIL-19100-F-04) is diaphragms, balls, seats, and gaskets or o-rings. An Air Kit is the air valve spool, pilot sleeve, gaskets, glyd-rings, retaining rings, shaft bushings, and grease. T-Series Air Kits still include the complete air valve assembly. Example wet SKU: 04-9804-51. Example air SKU: 04-9993-99-320.
What is an air valve repair kit on an AODD pump?
The air-end rebuild. Wilden calls it an Air Kit. ARO's PX15X IOM splits it into air section kit 637389 and major air valve assembly 637390-X. Order it for stalling, icing, or air blow-by, not for product at the muffler.
Are aftermarket diaphragm pump parts interchangeable with Wilden?
Nomad is a separate JDA Global aftermarket brand, not a Wilden line. Its current NPF manuals use N-prefix part numbers that mirror Wilden numbering, and distributors list the NPF pumps as Wilden-style. That is not the same as "every N04- part is in our cart." This site does not have a live Nomad-for-Wilden category. Send the Wilden SKU and nameplate and we will check current Nomad literature. For Graco, Sandpiper, Versa-Matic, and All-Flo aftermarket, use ThinQk; our ARO aisle is OEM only.
Buna-N vs EPDM vs PTFE vs Santoprene: which diaphragm should I use?
Oil and fuel: Buna-N (10-180 F). Dilute acids, caustics, cold weather: EPDM (-60-280 F) or Wil-Flex/Santoprene (-40-225 F traditional). Aggressive solvents and strong chemicals: PTFE (Wilden 40-220 F) or FKM (-40-350 F). Confirm housing material. Sources: Wilden WIL-19180-C-12, P4 EOM WIL-10183-E-04, Nomad NPF07/NPF25.
How do I read a Wilden P4 model number so I get the right kit?
Read P4/AAAPP/PUS/NE/NE as Pro-Flo 1-1/2 in, aluminum wetted/outer/air chambers, polypropylene center and air valve, polyurethane diaphragms, neoprene valve balls and seat o-rings (P4 EOM Section 2; catalog 04-11120). Then order a Wet Kit whose DDD elastomer matches PUS (or the diaphragm you are upgrading to) and an Air Kit whose ADS letter is P, not PS.
Get the Right Kit the First Time
If the nameplate is painted over, the pump is a mix of bolted and clamped generations, or you are not sure whether Nomad literature still covers that ADS, do not guess from port size. We will read the stamp, pull the OEM kit, and tell you when aftermarket is actually documented.
Photo of the nameplate (or the full model string).
Symptom: product at the muffler, stall, ice, or all three.
Fluid, temperature, and whether the duty is sanitary.
Whether you want OEM only or a documented aftermarket option.
Talk to an AODD parts specialist
Send the nameplate and the symptom. We will point you at the wet-end kit, the air-end kit, or both, and we will not invent a Nomad-for-Wilden category that is not on this site.