A sprayer gauge that bounces so hard you cannot read it, sits at 20 psi with the pump off, or never moves at all is a cheap part telling you something. Sometimes it is telling you the gauge is worn out. Just as often it is telling you the gauge was the wrong one for the job, or it is plumbed where it cannot read right. The trick is to figure out which before you screw in another one just like it.
Bleed the system to zero before you unscrew a gauge, and wear gloves; the gauge port is full of product.
1. Find out what the gauge is telling you
- Needle hammers back and forth with the pump running — pulsation from a diaphragm or piston pump, or a dry gauge on a bouncing boom. Needs a liquid-filled gauge, a snubber, or both.
- Needle does not return to zero with the pump off — the Bourdon tube is bent from an overpressure spike, or the movement is gummed with product. Replace it. A gauge that will not zero is lying everywhere else on the dial too.
- Needle is stuck, does not move at all — the port is plugged with dried product or the tube is split. Pull the gauge and look at the stem.
- Reads low and lazy on a cold morning, fine by noon — glycerin fill gone thick. Glycerin gauges get sluggish well above the point where the fill actually freezes.
- Reads different from the console or a second gauge — a Grade B gauge is allowed 3 percent of full scale error at the ends of the dial and 2 percent in the middle, so a 0-160 gauge can be off by almost 5 psi at 20 psi and still be in spec. Reading at the bottom of the scale is the problem.
- Fill has gone brown or the face has fogged — glycerin discolors with age and heat. Still works, but it is on its way out.
- Green crust on the stem, needle stuck high — brass wetted parts are being eaten. Wrong material for the chemical.
2. Why gauges fail
A sprayer gauge is a brass Bourdon tube on a brass movement behind an acrylic window. Pulsation flexes that tube thousands of times an hour, and on a dry gauge there is nothing damping the pointer, so the gears wear and the needle starts to wander. Liquid fill cushions the movement and keeps condensation off the dial. Pressure spikes from a boom valve slamming shut or a plugged strainer can push the tube past its yield point once and the gauge never zeros again. Fertilizers, especially ammonium thiosulfate and anything with chlorides, corrode brass and phosphor bronze; Hypro notes its brass-movement gauges are for media not corrosive to brass or bronze. And a gauge mounted on the pump outlet with no snubber, no isolation valve and the pump pulsing straight into it is being asked to do more than it was designed for.
3. The gauge for your sprayer
| Normal operating pressure | Gauge |
|---|---|
| 15 to 45 psi (most broadcast spraying, diaphragm pumps) | Hypro GG60 liquid-filled 0-60 psi, 2-1/2" stainless case; dry versions Hypro SG60 or Green Leaf SG060 2" |
| 40 to 120 psi (high-pressure booms, air-blast, spot spray guns) | Hypro GG160 glycerin-filled 0-160 psi, 1/4" bottom mount |
| Stainless case, dry, 60 or 100 psi | Valley CS-2141GXB60 2.5" stainless 0-60, Valley CS-2141GXB100 0-100 |
| Anhydrous ammonia | Hypro ASG60 0-60, ASG160 0-160, ASG1604 4" 0-160 |
| Gauge port on a 2" or 3" Banjo manifold line | Banjo M220YG45 2" full port 45° Y with 3/4" gauge port, M300YG45 3" |
| Reading pressure electronically on a Raven console | Raven 422-0000-119 pressure transducer, 0-250 psi, 1-5 V, Deutsch DT |
4. Picking and mounting it right
- Pick the range so your normal spraying pressure lands in the middle of the dial. The usual rule is that working pressure should not be more than about 75 percent of full scale, and the middle of the dial is where accuracy is best. If you spray at 30 to 40 psi, a 0-60 gauge is right and a 0-160 gauge is wrong, even though it will technically read.
- Liquid-filled for anything with a diaphragm or piston pump, anything on a boom, and anything outdoors where condensation fogs a dry gauge. Dry gauges are fine on a centrifugal pump at the tank where there is no pulsation and you only glance at it.
- Glycerin is the standard fill and is what Hypro uses, 99.5 percent pure in the GG series. It thickens in the cold; the common ambient floor given for glycerin gauges is around -20°C (-4°F), and silicone-filled gauges are the ones rated for colder work. For spring and summer spraying glycerin is fine. For a deicer rig that runs in January, look for silicone fill.
- Brass and bronze wetted parts for water and most crop protection mixes. For liquid fertilizer, deicer brine or anything that is attacking your brass fittings, use a stainless-wetted gauge or put the gauge behind a diaphragm isolator.
- Mount the gauge where the fluid is steady, not on the pump discharge elbow. Downstream of the regulating valve or at the boom manifold tells you what the nozzles actually see.
- If the needle still bounces on a liquid-filled gauge, add a snubber (a small restricted orifice fitting) between the port and the gauge. A partly closed 1/4" needle valve works the same way and doubles as an isolation valve so you can change the gauge without draining the line.
- A gauge is a wear item. If it will not zero, it is done. Check it against a known gauge or a transducer once a season.
If the gauge is right but the pressure is actually low, start with centrifugal pump won't prime or build pressure, and use the tip-sizing formula to confirm the pressure you should be running.
Not sure which gauge or range? Send a photo of the old gauge face and the port it screws into to sales@spraycenter.com or call (509) 838-2209.
Spray Center Electronics stocks Hypro, Green Leaf and Valley sprayer gauges and Raven pressure transducers in Spokane, WA. Part numbers here come from the manufacturers' parts sheets; if your gauge does not match what is described above, send a photo and we'll match it before you order.