A Raven rate controller that shows an erratic, low or zero flow reading while liquid is clearly going out the boom is almost always a flow meter problem, not a console problem. Inside an RFM meter there is a small turbine riding on a stud between two hubs, and a sensor in the end cap that counts the turbine's magnets as they go by. When the turbine drags, wobbles or stops, the count goes with it. Most of the time a cleaning or a cheap internal part fixes it. The trick is knowing which part, and when the meter is far enough gone that a new one is the better buy.
If the rate reads zero and the flow meter is a new suspect, read our Raven rate reads zero article first. It rules out speed, boom sense and cabling before you take the meter apart.
1. Find which part is failing
- Reading jumps around, worse at low flow — turbine dragging on a worn or fouled upstream hub bearing. Wettable powders and metal filings pack into the hub and the turbine stalls at low flow, then frees up as flow picks up.
- Reads steady but low, catch test comes up short — worn turbine blades or a worn bearing. The turbine is spinning slower than the liquid is moving. Rotor wear on the RFM 200 shows up this way after years of fertilizer.
- Reads zero, turbine spins free by hand — sensor (end cap / transducer) or cable. Raven's manual says that if the turbine spins freely and the meter still does not total, replace the flow meter transducer.
- Reads zero, turbine will not spin or wobbles — turbine stud, hub or end bearing. A broken stud or a cracked hub lets the turbine sit crooked and rub the housing.
- Reads fine, then drops to zero on rough ground — cable, not the meter. Check the Deutsch or Packard plug at the meter for backed-out pins and corrosion before buying anything.
- Counts with the boom off — turbine still turning from a leaking boom valve or product recirculating, or an installation with the meter close to a sharp elbow. The meter is doing its job.
2. Why it fails
The turbine runs on a plain bearing with product as the only lubricant. Dry powders, rust from a steel tank, teflon tape shavings and sand go straight through a 50 mesh strainer and into the hub. Running the meter dry or storing it with fertilizer in it eats the bearing surfaces. Raven's maintenance procedure says to flush the meter, pull the turbine and hub, clean out filings and wettable powders, confirm the blades are not worn, and check that the turbine spins freely with very little drag inside the hub. A 5 psi jet of air should spin it. If it drags, the stud is adjusted: tighten until the turbine stalls, then back off a third of a turn (a sixteenth of a turn at a time if it is still dragging). Also confirm the arrow on the body points with the flow.
3. The part for your meter
When to replace the whole meter. If the housing is cracked, the flange face is chewed up, the turbine has eaten into the bore, or you are on your second rebuild in two seasons, buy the meter. The repair kit on a 60P is about a fifth of the meter price, so one rebuild always makes sense; two does not. Current meters: RFM 60P 063-0171-985 (replaces 063-0171-793), RFM 100P 063-0173-578, RFM 200P 063-0173-579 (replaces 063-0159-751), RFM 60S HP stainless 063-0173-867, and the RFM 15 063-0172-058 for low-rate work. The poly 60P, 100P and 200P are all M200/M300 flange, so they drop in where the old meter sat.
4. Doing the rebuild
- Bleed the boom and nurse hose and rinse the meter before you open it. Gloves and eye protection; what is in there is concentrate.
- Mark the flow arrow before pulling the flanges. Meters get put back in backwards more than you would think.
- Lay the parts out in order. The upstream hub, turbine, stud and downstream hub only go together one way, but the clips are easy to lose.
- After the stud adjustment, blow through the meter with low-pressure air. If you can hear the turbine whir up and coast down, it is right.
- Check the cable before you condemn a sensor. Raven's test: set METER CAL to 1, booms on, and jump the ground and signal pins at the meter plug with a paper clip. Total volume should tick up each time. Then put the real METER CAL back.
- Any time the turbine or hub changes, do a catch test. Our flow meter cal and catch test article walks through it.
- A 50 mesh line strainer ahead of the meter is cheap insurance. If you run dry products, flush the meter at the end of every day.
Not sure which RFM part you need? Send a photo of the meter tag and the turbine to sales@spraycenter.com or call (509) 838-2209.
Spray Center Electronics stocks Raven RFM flow meters, turbines, hubs, bearings, sensors and cables in Spokane, WA. Part numbers here come from the manufacturers' parts sheets; if your meter, boom or fittings have been changed over the years, send a photo of the tag or the part and we'll match it before you order.