on-demand pump problem

[woodlot]

Can anyone explain this or help out......

I have an ATV with a sprayer that I use for spraying Round-Up and other herbicides. The sprayer is 25gal and has a 12vdc pump. The pump is connected directly to the ATV battery, and has an internal pressure switch set at 60PSI. Its an "on-demand" pump.

The pump works great when the ATV is OFF. However, if the ATV is at IDLE the pump short cycles. In fact, it short cycles so fast that it "pluses" (like on & off a few times every second.)

I'd like to get it so the pump runs constantly and smoothly all the time. I can't shut off the ATV every time I stop to spray. I'm not sure where to start......Thanks.

 

[JerryG]

If the pump has too much volume for the number of nozzles or has the flow restricted too much, it will cycle fast.

 

[Highbeam]

In the RV world people actually install the small blue expansion tanks made for installation right above your residential water heater. The expansion tank softens vibration, sound, and reduces cycling of the pump.

 

[RonMar]

So if I understand you correctly, you are using a hand spray wand connected to the on demand pump. When setting with the ATV off, Shortly after you start spraying, the pump starts to run and stays running untill you stop spraying then the pump stops shortly afteward. With the engine running, you start to spray and the pump cycles on and off rapidly while you are spraying.

Believe it or not, that actually sounds normal to me if your battery is a little weak/old. With the engine off, the pump pressurizes the system and shuts off. When you start to spray, the pressure drops and the pump turns on to try and make up the pressure. With the engine charging system not adding power to the battery, the voltage drops a bit and the pump is unable to keep up with the flow demands of the spray wand so the pump runs constantly and the pressure drops to a point that the pump can maintain. Since the pressure never reaches the shutoff point, the pump runs constantly. If you have a pressure gauge on your system, you will see that the pressure drops to a point and stays there. As the battery discharges, that pressure will get lower and lower. With the engine running and the battery being maintained at peak voltage, the pump is easilly able to meet the demand of the spray wand so it shuts off. Since the wand is still spraying, the pressure quickly drops below the turn-on point of the pump so it does and quickly boosts the pressure above the turnoff point.

How to fix this? It could be that the voltage regulator on your ATV has a problem and is not regualting properly. Do you have a volt meter? The regulator circuit of most ATV's/motorcycles should give an output of 14.5 VDC +/- 0.5 VDC even with the load of headlights and pump running. If you are getting more than this voltage measured at the battery with the pump running, you may have charging issues. It is also possible that the setpoint on the pump pressure switch is too low. If you don't have one, I would reccomend adding a pressure gauge "T"d to the pump output. If the switch is set below the pump rated maximum pressure, it might be possible to turn it up slightly so that the pump would have trouble reaching the shutoff pressure with the engine running when the wand is spraying as it does when the engine is shut off. Of course I DO NOT reccomend seting the switch above the maximum pressure rateing from the pump manufacturer as the pump could damage itself trying to reach this pressure when not spraying You could add a bigger spray nozzel so that the pump when connected to the running ATV is unable to meet the flow demand of the spray wand and still make the pressure go high enough to turn off the pump. You could add a pressure regulator to the pump output that maintains the output pressure below the switch setpoint and diverts the excess back to the tank. This would mean that the pump runs all the time. You would then manually turn it on when you want to spray and off when you don't. You could also switch to a lower volume pump that would be unable to maintain max pressure with full ATV charging voltage when the wand is spraying.

 

[gregoryd]

I have a Moose brand sprayer with a Filmco pump and had the same problem until the pump burned out --- come to find out, there is a bypass valve after the pump which has a hose running back into to tank.

If yours is equiped that way, turn the bypass valve on slightly so when you are spraying, the pump runs constantly instead of cycling. The bypass setup is also used to lower the pressure in which the boom or handheld is spraying at.

Hope this helps.

 

[woodlot]

Thanks for the insight guys, I think RonMar nailed it. BTW, here's a link to my sprayer: http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_640_640

So, my options are:

• Adding a tee to create a bypass back to the tank.
• Getting a diffrent hand-wand that will put out more GPM.
• Adjusting the pressure switch

Adding a tee sounds good, but won't the pump short-cycle when I'm NOT activating the hand sprayer? I'm assuming the tank side of the tee would need to be turned down pretty far, otherwise I wouldn't get much out of the hand wand.....correct? I think adding the tee would solve one problem (stopping the short cycling WHILE spraying) but would create another problem (short-cycling when NOT spraying).

Getting a larger (more GPM) hand wand sounds easy too. Unfortunitly my supplier does not list MAX GPM for the basic hand wands. I'd be shopping in the dark.

I'm not sure if the internal switch on the pump is adjustable. The plate on the motor housing says its pre-set to 60psi. I'm not sure that I'd want to increase past that. These ATV set-ups don't look like there made for much more than that ( all platic parts, etc.)

These were some great suggestions, I'm not sure they would work.

 

[RonMar]

If you add the "T" or a "Y" gate valve assembly and recirc liquid back to the tank to lower the pressure, you will have to manually switch the pump on and off(switch on, spray, switch off) when you want to spray, or the pump will cycle on its own when not spraying. You will just need to add a remote power switch on the ATV. The "Y" gate valve with one leg feeding back into the tank is how I regulate the spray boom pressure down to 20PSI on my Fimco 25 gallon sprayer. I control the sprayer with an inline power switch from the seat and the pump runs whenever the switch is on. If I close both the "Y" valves to the boom and the recirc to the tank, the pressure quickly builds till the pressure switch shuts the pump off at around 60 PSI. My spray wand is "T"d off between the pump outlet and the "Y". The "Y" used on my sprayer is just a regular plastic garden hose "Y" connection with valves built into the outlets.

 

[woodlot]

If I close both the "Y" valves to the boom and the recirc to the tank, the pressure quickly builds till the pressure switch shuts the pump off at around 60 PSI.

Ahh, yes RonMar. I overlooked a simple solution. When I'm NOT spraying I could just shut-off the tank by-pass at the Y-fitting, thereby letting pressure build and allowing the pump shut off at 60psi. No extra switch needed. Then when I start to spray I'd just open it enough to let the pump run continuisly.

This would be a minor pain, flipping a valve every time I start or stop spraying, but I think I'd get acustomed to where the valve needs to be, and over time it would become automatic. I could even put some type of flow restrictor in the bypass tube, that way I'd just have to flip the valve full-on or full-off.

Best of all its an easy, inexpensive fix. Although I think I'll need to drill a hole into my tank for the bypass tube. Do you terminate the bypass tube near the bottom of the tank (under the fluid level)? What kind of tube did you use?

 

[RonMar]

My sprayer came already plummed this way. The recirc line on mine is just a piece of 1/2" hose that runs to just inside the top of the tank. Personally I think it would be easier to set the recirc valve and turn the pump on and off electrically than by using the valve. My sprayer is however on a trailer behind the lawn tractor so I can't reach the valves when seated.