When a centrifugal pump won’t pick up or the pressure has fallen off, it’s tempting to order an impeller. Most of the time the pump is fine and something on the suction side or the drive is the problem. Check these in order; they cost nothing.
Won’t prime, or loses prime
Most centrifugal pumps are not self-priming. They need liquid flowing into them, and any air getting in on the suction side will stop them from picking up.
- Mount it below the tank outlet so liquid flows to the pump by gravity, and fill the pump body before starting. (Self-priming models, like Ace’s SP pumps, are the exception.)
- Find the air leak. Check every suction fitting, hose clamp and o-ring between the tank and the pump. A leaking shaft seal also lets air in. A suction hose that collapses under vacuum acts like a closed valve.
- Clean the suction strainer.
- Check valve. If your pump has one, make sure it’s there and seating, so the pump body doesn’t drain back to the tank.
Low pressure or low flow
- Restriction on the suction side. A plugged strainer, a kinked or undersized suction hose, or a half-closed valve starves the pump. A gravel-in-the-pump rattle under load is cavitation; it means the pump isn’t getting enough liquid.
- Speed. Centrifugal output drops off fast as speed drops. On a gas engine pump, run full throttle. On a PTO belt drive, check belt tension and PTO speed. On a hydraulic pump, check the tractor’s oil flow setting against the motor rating — see matching a hydraulic pump to your tractor.
- Air in the suction, same as for priming. Air makes the pressure surge and drop.
- Then the impeller. Pull the volute and look. Chipped or worn vanes, debris wrapped around the hub, or a worn wear plate on pumps that have one all cut pressure. Make sure the impeller is turning the right way after any rebuild.
Which impeller?
Impellers are sized to the pump and the drive. Ace makes most of its pumps with a choice of Valox, cast iron or polypropylene impellers (the CI and PI suffixes), and Banjo uses different vane counts for different engine sizes. The safe way to get the right one is to look your pump up in the Pump Finder and pick “Low pressure or flow”: it lists the impeller, wear parts and o-rings for that exact model. A few common ones: FMC-200-HYD-304, 200PH6, 9306C-HM5C.
Noisy or vibrating
Turn the shaft by hand with the drive off. Rough or notchy means bearings. A scraping sound can be the impeller rubbing the volute or wear plate. A rattle only under load is cavitation; fix the suction before replacing parts.
Still stuck? Call (509) 838-2209 with the model off the tag and what the pump is doing, or ask Dusty, our parts assistant, on any page of the site.
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.