Pump cavitation running dry

So yesterday for what seems like the 10th time since I’ve had the new machine, the buffer tank ran low. We are really good at detecting it and at the very first sight of even the smallest sputter lay off the trigger. We let the tank fill back up a bit before using again. I have a general pump 7.8gpm (hydrotek machine specs). I got worried as I tried to spray again with 12” of water in the buffer tank and and it just pissed out slow. I heard a little rattle noise from the pump area (hard to tell as it’s so loud over there from the motor) and checked the bypass hose it was not even pouring anything out. I turned the machine off (was running and spraying all day) let it cool down. I checked my hose connections and banjo filter on the supply side and it was clean. The pump had full oil. The belts were on good. The pressure hose outputs were fine. Fired it back up about 20-30 minutes later and it still pissed water for a few seconds but then came back to life and worked just fine. I’m wondering if the slightest time of not having water fed through it (essentially an air bubble as it’s never been ran for more than 2-3 seconds without water) is enough to fry the pump? I know cavitation is a big no no but I have no idea to what degree is considered dangerous? I know udor can be run dry for a short period of time and be fine. Would having an air bubble or running out of water for lets say 5 seconds be considered running dry?

I work out big air pockets multiple times in a day. The pump seeing air here and there is not going to chew on the seals like sucking lil air bubbles. Cavitation is very different. If you’re worried about it you can make up a adapter and pressure feed it with water to work the air out. But it’s really not needed.

If you run it dry you need to prime it again. I wouldn’t sit there and let the machine run for a half hour while it’s just barely trickling out the end trying to get it primed. Shut it down, pull your hose off your pump, and get the air out. If you’re going to keep running it dry maybe you need a low water shut off switch for your machine.

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Don’t Wait until your gun starts sputtering before you check your tank. Get in the habit of checking it more frequently and quit letting your tank run dry. I never let my tank get below 50 gallons before shutting off the machine and letting the tank refill.

You’ll also need more head pressure from your tank to get a faster prime if you have plenty of air in it. 12 inches isn’t jack, you get 2.3 psi per foot so you’re looking at about 11psi


Ain’t no huge deal man. It happens to us sometimes, The pump is trying to prime itself the sputter is air in your system, get a good amount of head pressure in your tank ,fire it up and wash on and try to keep a better eye on it. It’ll prime itself. I’m not saying its good to let it run dry , But it happens.
Btw. if you can throttle your machine down it will prime faster, thats how we suck in antifreeze in the winter via 3 way ball valve ,Air is always in the antifreeze line at first.

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Dont you have that strange electric valve set up you may be causing your own problem by pushing air into your tank.

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I won’t let it continue to run if it’s dry. Will shut it down, let it fill a bit and turn back on. What I have been doing wrong is trying to time turning off the water so that I can use up most of what’s in the buffer tank to clean with rather than dump and waste water in the street (where I can also get a ticket for chlorinated water going into storm drains). I keep using what’s left up faster than expected. I want to install a second electric float switch (just. 12v mini float switch that mounts on the side of the tank) and put that one 12” up from the bottom of the tank and connect it and the other one to a 3 way toggle switch so that when we are getting close to wrapping up the job I can switch it to the lower float and have it keep the water at 12”. 95% of the time the house pressure is enough to keep up with the 7.8gpm I run.

You mean just pull the pressure hose off and run it to work the air out? This happened to me today, house had a well, very slow water, i took the risk trying to finish the job with low water in buffer tank for longer than i should have as i was tired of waiting and not making money. Now it vibrates and i get maybe half the flow of water out the gun. If it half-works does it mean the pump is not ruined?
I must add i definitely pushed my luck and ran it for more than a few seconds that way as i was Almost Finished, just had to finish rinsing a corner and i got impatient as i kept waiting for water.

No. That’s not what that means. Start with a full buffer tank for good head pressure, disconnect the whip line from the reel, set machine idle all the way down, start machine and let it idle for a couple minutes to purge the air. Slowly idle it back up and see if you’re good to go.

Go ahead and buy a packing set and keep it on the trailer or in your truck or whatever. You’re going to need them eventually.

Thanks i’ll try that. I hope the pump is still good. I’ll try to find a “packing set” online now.

What pump do you have?

If it was for a very short time, the pump is probably okay. Could be a number of things but my guess is you have an air pocket between the buffer and pump. If not that, could be a stuck check valve(s) or you chewed up the seals or even possibly cracked a plunger(s). All are easy fixes once you have the right parts and tools.

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Never bought from this site before but they show pretty much every serviceable part for that pump.

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Also, don’t spend $80 on a pump seal “extractor”. Just get a set of snap ring pliers that protrude out from the side. Like these:


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If i killed the pump it’s just bolts to remove, change pump and rebolt?

Looks like youtube and i have a date.

The pump only dies when your crank is poking out the side of the case. That rarely happens. The manifold is the brass portion held on by eight hex head bolts and can be fully rebuilt unless the brass has cavitated to the point where the new seals won’t form a proper seal around the plunger (piston). In that case you have two options: buy a new manifold and slap it on or just bite the bullet and get a new pump. Typically, on those cheaper pumps (quality, not price) it’s just not worth replacing the manifold. At that point just buy a new pump and be done with it.

Really not even necessary to replace seals. Just do one cylinder at a time and pay close attention to the orientation of each seal as you remove it and put the new ones in in reverse order but exactly the same orientation. If you get into and need help just PM me and I’ll shoot you my phone number.

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