Pressure fluctuations, trigger gun problems and pop goes the relief valve

[Bennyhonda 14]

Murphy has come to visit me at the jobsite far too often this month. Aside from the Landa needing new bearings, I have a new issue to contend with.

While using the burner for the first time this year, I noticed while spraying down some walls that the pressure would fluctuate. It would begin by pressuring down to a gentle mist for a few seconds followed by a gradual buildup and then what seemed like an overpressure burst and then get back to normal. I noticed that a couple of times this happened, the over pressure burst would also create steam coming from the tip. (the thermostat was set at 200). I also noticed that the trigger gun would sometimes have trouble shutting off entirely. I would weep from the tip with a small stream before turning off. Other times it would shut off as soon as it was released. I thought maybe I had something blocking the nozzle or gun so I switched them out and the same thing happened with the other gun.

No noticeable pressure problems with the surface cleaner. At the end of the day I set the gun down and reeled up the supply hose. Boom! Hissssssssssssssssssssssssss... there goes the pressure relief valve.

I had a job the next day so I replaced the valve. I did not use the heater though I would have liked to. I checked the unloader and the pressure seems to be regulated correctly. The bypass was functioning as it should as well. I had the pressure guage on all day and the problem never repeated itself.

I had a couple things in mind to try. First of all have a replacement unloader that I thought I'd try. I also thought I'd try descaling the coil in the event there was an obstruction there. Is there anything else I should consider?

[Alexy 85]

You probably have a ton of scale and/or rust in your burner and the first time you used it a bunch of it let go and clogged the gun valve the unloader and went all thru your hoses. Sounds like you have cleaned it all out. I would run the machine with the burner ON and no gun for a few mins and let it run the water thru. Put a clean white 5 gallon bucket and look and see what comes out. You can have brown or black water from rust and scale in there or just some chunks of what-ever is still in there.

[Doug T 19]

I would check that the burner is not on when the gun is off...sounds to me like you are getting steam then as you hold the gun on it the water gets back to normal temps.

[mick m 19]

Do you run the water thru the heater all the time even tho it's not turned on?, or do you only connect it when needed? If it's the latter, then it probably is built up scale/rust trying to get out. If it's the former, have you got some dirty water from somewhere?

[Russ Johnson 141]

I would check that the burner is not on when the gun is off...sounds to me like you are getting steam then as you hold the gun on it the water gets back to normal temps.

That's what it sounds like to me. The burner is probably staying lit with the trigger closed and overheating the water. A very dangerous situation.

[Bennyhonda 14]

The unit runs water through the coil whether the burner is lit or not. I wouldn't think junk in the line would make steam, would it?

I was leaning towards unloader problem but I'll go test that again today with a couple new things I learned off youtube. The burner staying on was also one of my thoughts so I've ordered a flow switch to replace the pressure switch that's currently on the unit. Also noticed that two of my jumper hoses are weeping now, the one from the pump to the coil and the coil to the hose reels. Also purchased replacements for those. I assume they were damaged in the over-pressurization. I think this may have been why the guns were not working... they didn't seem clogged. I think the pressure was so great that the valves couldn't close.

On another note, when I had the pressure valve hooked up(near the gun), I noticed that it consistently read 3000psi when in bypass mode. When I pulled the trigger gun it would drop to and hold at 800-900 psi. This doesn't seem right, does it? According to my calculations of 100psi loss per 50f and with the 250ft of high pressure hose I'm using, it should be more like 2500psi. I'll try it again with a 50' and see what it reads.

Any other ideas or info would be appreciated as are the previous suggestions. Thanks.

Edited May 18, 2013 by Bennyhonda

[mick m 19]

Sorry Ben, I was refering more to the pressure problems, rather than the steam. Someone had this exact same problem a couple of weeks ago & it turned out he had cracked pistons. Almost the same symptoms as yours in regards to the pressure fluctuations. Is your gun pulsing with water flowing thru it?

[happysmobile 14]

Sounds like the unloader. Maybe junk getting struck in it. I would start there and if that didn't help pull the head off. You would think the unloader would keep the pressure from getting high enough to blow the safety if it was the case of the burner staying on. Wouldn't hurt to check that while you were in there. Good luck.

[Bennyhonda 14]

The gun doesnt pulse like I've seen on some videos. It will work fine for an hour and then all of a sudden, go low for a few seconds than go really high which is sometimes followed by full on steam discharge. I stopped using the heater and everything is back to normal. Just replaced hoses and a bunch of fittings today. Hope to test it out tomorrow.

[Douglas Hicks 128]

You may also have a bad hi-limit swtch. It should be at or near the outlet of coil., just before the hose connection.

[Bennyhonda 14]

Well, I replaced the unloader, pressure switch and three weeping whip lines. What a difference the unloader made. It acts like a pressure washer again. Still need to work out the burner situation but I'll start on that when the flow switch arrives. Do you guys think I should just cut the lines on the old vacuum switch and leave it on the pump? Shouldnt hurt anything and save me the need to pickup a plug for the hole. As for the high limit switch, I'm not sure which one is on my unit (if any). I will check it out though.

[Badzuk 16]

Do you guys think I should just cut the lines on the old vacuum switch and leave it on the pump? Shouldnt hurt anything and save me the need to pickup a plug for the hole.

I would remove it, it you leave it on you risk sucking air in through the damaged diaphragm and causing more problems than picking up a plug.

[Bennyhonda 14]

Thanks Jason. You reminded me that it's a vacuum system that can leak.

[ttmoney 14]

Murphy has come to visit me at the jobsite far too often this month. Aside from the Landa needing new bearings, I have a new issue to contend with.

While using the burner for the first time this year, I noticed while spraying down some walls that the pressure would fluctuate. It would begin by pressuring down to a gentle mist for a few seconds followed by a gradual buildup and then what seemed like an overpressure burst and then get back to normal. I noticed that a couple of times this happened, the over pressure burst would also create steam coming from the tip. (the thermostat was set at 200). I also noticed that the trigger gun would sometimes have trouble shutting off entirely. I would weep from the tip with a small stream before turning off. Other times it would shut off as soon as it was released. I thought maybe I had something blocking the nozzle or gun so I switched them out and the same thing happened with the other gun.

No noticeable pressure problems with the surface cleaner. At the end of the day I set the gun down and reeled up the supply hose. Boom! Hissssssssssssssssssssssssss... there goes the pressure relief valve.

I had a job the next day so I replaced the valve. I did not use the heater though I would have liked to. I checked the unloader and the pressure seems to be regulated correctly. The bypass was functioning as it should as well. I had the pressure guage on all day and the problem never repeated itself.

I had a couple things in mind to try. First of all have a replacement unloader that I thought I'd try. I also thought I'd try descaling the coil in the event there was an obstruction there. Is there anything else I should consider?

It's not good to let the unloader unload for more than three minutes. I found that some of my crews where setting up as they should including firing up the pressure washer. Kept having this problem even on pumps that where only a month old. Made sure everyone knew the pressure washer only runs for 1 minute without you pressure washing problem solved.

[Chemical Doctor 15]

It's not good to let the unloader unload for more than three minutes. I found that some of my crews where setting up as they should including firing up the pressure washer. Kept having this problem even on pumps that where only a month old. Made sure everyone knew the pressure washer only runs for 1 minute without you pressure washing problem solved.

This is why we always setup our trailer units with the unloader bypassing back to the water tank. This eliminates many problems. It will save you lots of money in the long run. I have always advised people using a portable machine to have a ball valve between their hose and gun to simply detach the gun and open the ball valve if they need to lay the gun down for more that two minutes. This way the water will just run out on the ground and they will not have to worry about the problem. As always, if you are close enough to the machine just turn it of.