A centrifugal pump that drips from behind the body, between the pump and the motor, engine or frame, has a worn mechanical shaft seal. It’s the most common pump repair there is, and the parts are inexpensive. The trick is making sure it’s really the seal, and ordering the seal that matches your pump.
1. Find where the drip is coming from
- Spray mix from the gap behind the pump body (or a weep hole in the frame) — the mechanical shaft seal.
- Drips at the joint where the housing meets the frame, or at a drain or prime plug — an o-ring or gasket, not the seal. Cheaper fix.
- Oil instead of spray mix on a hydraulic-drive pump — the hydraulic motor’s shaft seal. That’s a motor kit, covered in hydraulic pump problems.
- A crack in the housing — usually freeze damage. Replace the housing.
2. Why seals fail
Running dry is the big one: the seal faces are cooled and lubricated by the liquid, and even a minute without it can crack the ceramic or burn the faces. Abrasive mixes (wettable powders, some fertilizers) wear the faces too, and harsh chemicals swell the wrong rubber. If you’re replacing seals more than once a season, look at a silicon carbide or severe-duty seal, and make sure the pump can’t run without liquid.
3. The seal or kit for your pump
| Pump | Seal or kit |
|---|---|
| Ace FMC pumps | BAC-7V carbon/ceramic Viton seal, or the full kit: RK-FMC-150 (150 pumps), RK-FMC (200 and 1-1/4" pumps) |
| Ace FMCSC pumps | BAC-7SC silicon carbide seal, or RK-FMCSC-150 / RK-FMCSC |
| Banjo 2" and 3" poly (200PO, 300PO, M220PO, M300PO, 200PH, 200PHY) | 12713; 12713V for FKM (V) models; 12713SD severe duty |
| Banjo 2" cast iron (200POI, 200PBI, 200PIH) | 17035 or 17035SD |
| Banjo 3" cast iron (300POI, 300PIH13) | 18025 or 18025SD |
| Banjo poly wet seal (W models) | 15035E |
| Hypro cast iron 9203 / 9303 / 9306 | 3430-0332 standard seal kit, or 3430-0589 silicon carbide |
That covers the common ones. For anything else, or to check yours, open the pump in the Pump Finder and pick “Leaking at the shaft”: it lists the seal, the kit and the o-rings that go with it for that exact model, with prices and an add-to-cart button. For example: FMC-150F-HYD-206, 200PO, 9303C-HM4C.
4. Replacing it
- Replace both halves of the seal together (the rotating head and the stationary seat). Mixing an old seat with a new head is the most common reason a new seal leaks.
- Replace the o-rings and gasket you disturb while you’re in there. The kits include them.
- Don’t touch the seal faces, and keep them clean. Wet the rubber parts with clean water to slide them on; don’t use grease or oil.
- Look at the shaft or shaft sleeve where the seal rides. Grooves or pitting there will chew up a new seal.
- Prime the pump before the first start so the new seal never runs dry.
Not sure which seal is in your pump? Send a photo of the pump tag to sales@spraycenter.com or call (509) 838-2209.
Spray Center Electronics stocks pump parts and repair kits for Ace, Banjo, Hypro/SHURflo and Annovi Reverberi (AR) pumps in Spokane, WA. Part numbers here come from the manufacturers’ parts sheets; when your pump has been modified or the tag is gone, send a photo to sales@spraycenter.com or call (509) 838-2209 and we’ll match it before you order.