Newbie is having trouble controlling Burner temp

[Badzuk 16]

Thanks in advance for any Help you can give...

One of my machines has a vertical burner on it. The issue I have is that once the water flow is stopped (and the burner is shut down) the temperature of the water in the coil continues to rise.

The burner does a good job of raising the water temp about 90-100 degrees, and maintains that as long as the water flows. Once you release the trigger, the pump goes into bypass and the burner shuts down, but the temp continues to climb. When I tested it yesterday I had a temp reading of 230 within 5 minutes of the pump in bypass.

It seems that the water continues to absorb the heat from the coils and burner.

Any Help or ideas?

[Guy B 70]

This is why there are pressure relief valves or pop off valves on hot water PW's. It just happens and I'm not sure you can do anything about this, unless you just cut the burner off and run some cold water through the system. Once off the gun and burner cuts off the water is "Trapped" behind the unloader in the coil. Water in the coil absorbs the left over heat of the metal coils and will raise the water temp in the coil. Most coils are sch. 80 pipe which is heavy duty and takes a lot of psi to burst them. If the temp does get to high, the thermal relief or pop off valve will open and pressure is relieved from the system.

For the record I've been using hot water skids for 5 years and have never had a problem.

[Douglas Hicks 128]

Would this also happen if the insuilation was fuel soaked or fuel was puddling in at teh bottom of burning chamber, and continued to burn?

[Guy B 70]

Possibly, but if that happened there would be a lot of smoke or a strong fuel smell.

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[Beth n Rod 1,279]

If you don't have a 30gal+ reserve tank for the water to flow into before recirculating, it will build up heat just from going through the pump.

This has nothing to do with the burner or absorption of heat from the coils. it has to do with the friction of the pump as the water flows through it. That is why it is recommended to pull the trigger every 3 minutes or so to keep the pump cool by allowing the trapped water in the system to exit and cool water to enter the loop.

Rod!~

btw, you don't want to rely on the high temp pop off valve either. Every time this is used, it brings the water close to the threshold of damage to the pump and its packings.

Edited October 12, 2011 by Beth n Rod

[Badzuk 16]

Thanks for the replies, I appreciate the help. The burner is after the unloader, so the bypass water is not moving through the coil at all. Once the flow is stopped the water in the coil doesn't flow.

I have 5 machines that I run, 3 are Alkota, one is an old north star, and one is an electric drive unit. All my machines run the General pump (4GPM 3500psi), and all but the electric unit use a 13 hp Honda motor. All units have diesel fired burners, and the north star is the only one that is vertical.

I've only been managing the hood cleaning division for the past year, and our "mechanic" does some interesting work when repairs are needed, so I've recently took over most of the repair work so that it can be fixed right and not cobbled together.

I need to bring these machines back up to par, I can't have one of my guys getting hurt because we removed a safety valve or something stupid like that.

What is the correct plumbing for these machines? What safety measures/items need to be in place? It looks like most of the safety valves have been removed as they failed (scary).

Currently water flows as follows Pump, Unloader, Flow Switch, Burner, then out to the hose and gun. I would like to install a thermostat and high pressure relief valve, but what else should I be looking at.

[Guy B 70]

Good call Rod. I thought that because these are hot water machines they would have a buffer tank.

Buffer tanks are plumbed so water doesn't continually bypass through your pump causing heat build up. With a buffer tank water bypasses to the tank and lower temp water is pulled to the pump from the tank.

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Edited October 12, 2011 by Guy B

[Scott Stone 604]

The burner has mass, and the coil is heavy steel. It acts as a heat sink, and the more mass there is, the longer it is going to transfer the heat to the water. One thing you might try to reduce this problem is to descale your coil. It will make it run much more efficiently, and reduce the heat sink effect. Other then that, it is what it is. Just remember to let it cool down a bit after you turn off your heater.

[Douglas Hicks 128]

Start by getting service manuals from the mfg for each machine. You will need wireing diagrams and pictures of the mechanicals, and contact information. Then, contact some of the advertisers. Deluxe from Texas is a company I have used, and will continue to use. Bob from Pressure Tek is good. Some have used EnviroSpec, do a search for the experience others have had with that company. Russ from Southside is a good perosn to know. http://www.thegrimescene.com/forums/look-whats-new/6611-vendor-links.html A service company close by can be valuble.

[Badzuk 16]

Thanks for the help.

Has anyone completely rewired their machine? Some of the previous fixes on these machines have really left a lot to be desired. I would like to make a new control box with a few indicator lights (main power, flow switch on, thermostat on, burner on) and some fuses to protect everything. Maybe even include a test switch to bypass the controls to test the burner. I'm thinking a terminal strip to make it simpler to replace the flow switch and thermostat.

Currently I have an on/off switch and a flow switch, no lights, fuses, or thermostat. There is a relay in the circuit.

Or does someone make a control box similar to this that I can install?

Thanks again...