Weed Sprayer - Bad Design Cost Money, Downtime

Posted by Andrew Greess on Mar 19, 2013

Weed control sprayer brought in with pump issues. Weed sprayer pumps were having problems, jobs were being missed. Because of the bad plumbing design, we couldn't remove the pumps to start diagnosing them without dumping lots of herbicide in the street.

Here are the details:

2 large tanks, 2 diaphragm pumps, 2 motors. Diaphragm pumps are positive displacement pumps. They need a pressure relief valve to dump the material back into the tank when the tech is not spraying.

Two of the major diaphragm pump manufacturers (Hypro & Udor) require that the return dump back into the top of the tank, unimpeded. Putting the return at the bottom of the tank, creates back pressure (from the weight of the water in the tank) on the pump, which the pump is not designed to handle. Back pressure can affect pump performance and could void the warranty (though i have never seen the later occur).

Here is what we found:

weed control sprayer bad plumbing designTop hose is for agitation. There is no shut off valve on this line. There should be.

Middle hose is the pressure relief/return. It should be at top. Can't put a shut off valve on this line because if some started sprayer with valve closed, something would blow. This is another good reason to put the return at the top of the tank.

Bottom hose (largest hose) is the suction hose. There is a shut off on this line. Yippeee!

Here are the problems we identified:

1. no shut off on agitation line or return line. if we removed the pump, chemical would spill out of the tank until we were able to cram enough stuff in the 2 lines (agitation, return) or until it drained to the bottom of the lower tank penetration.

2. return line to bottom of tank violates manufacturer installation instructions and is just not a good idea.

3. One diaphragm pump was run with burst diaphragms for extended period. Pump was a total loss.

4. Overfilled gear box oil on second pump, disguising a gear box problem that should have been addressed sooner.

5. We would never put the agitation this close to the suction line. There is a pretty good chance of the agitation interfering with the suction at some level of liquid in the tank. Agitation should probably have been installed on the other end of the tank.

6. The pumps used on this vehicle were (are) high quality pumps. The problem was that the were not pumps commonly used in AZ. This meant that parts are not readily available.

7. Client had to take truck away and run pumps that shouldn't have been run, in order to get the remaining chemical out of the tank.

Other than that Mrs. Lincoln, how did you like the show?

Here is what we did:

Here is the relief line going into the top of the tank:

1 Weed Control Sprayer Plumbing

Here the bottom of the tank:

- Shut off on agitation line. Didn't move agitation because someone would have had to climb into the tank to install the fitting.

- Plug old penetration for relief line.

1 jsw weed control sprayer bad plumbing design 2Now when the pump needs service, it doesn't matter if the tank is full. Pump can be removed with no spill because both lines can be closed.

I don't care how much they saved buying this landscape sprayer, it wasn't worth it.

Comments invited.

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