pressure gauge location

findmyselfacity

Hello all,

I am having trouble maintaining temperature in a wash tank on a commercial dishwasher. The steam coil is submerged in the water in the tank. A solenoid coil allows steam to enter the coil when called for, air and condensate are handled by an inverted bucket trap.

The tank next to it has a similar setup, and has no heating issues.

I have nearly zero lack of access to anything, (I could only pull the strainer and it was clean, cannot access the solenoid valve), so my last troubleshooting step was to install a pressure gauge after the coil and before the trap. According to the incoming gauge there is an average pressure of 22 psi, the gauge I installed shows an average of 7 psi, after being allowed to call for heat for a bit. It's near zero at 1st.

Are the readings from this gauge installed after the coil and before the trap of any use at all?

Thank you for any and all insights and responses.

Mark Walnicki

ScottSecor

I'm not sure I follow you. If I understand correctly, your saying the incoming pressure is more or less a steady 22 psi and the pressure to on the outlet of the steam coil is zero when the steam solenoid initially opens. Once the dish washer warms up the coil pressure ultimately rises to 7psi. I may be wrong, but I'm assuming the coil is filled with steam and this coil in turn heats large amounts of cold city? water.

If I'm correct, the gauge after the coil is certainly better than nothing. It tells us the coil is likely intact (but could be fouled), the solenoid valve is opening (not sure how much), etc.

The fact that the strainer was clean tells us that the coil may also be clean on the inside, however it is possible the exterior of the coil is fouled (dirty, covered with minerals). If your actually losing 22 psi and the supply and return are not restricted in any way, it appears that you are consuming a lot of energy (that's what you want).

We don't do a lot of high pressure steam these days, but I believe inverted bucket traps are best when used with a steady load. Not sure if a dishwasher is considered a stead load, depends on the site I suppose. However since the second unit is working fine, I'm guessing the trap is ok for this application. I suggest opening up the outlet of the coil if at all possible (safely) and seeing if there is adequate flow. If flow is good I'd suggest the exterior of the coil may be an issue. If not perhaps the return is slightly pressurized and the large differential is not enough to overcome the difference? If the latter is the case, I suspect there are other failed traps in the line.

findmyselfacity

Scott, thank you very much for your response. You are correct, the coil fills with steam and heats the water surrounding it. 3/4" in and out, and uncoiled it would be around 30' long.

I forgot to mention that at one time I had nearly 15 psi on the gauge I installed, but from what I am understanding from your response, it's ok for the pressure to change, will change based on what's happening to the steam in the coil and the greater the differential, the more energy that has been released and transferred to the water.

I have previously undone the union after the trap to eliminate other traps, check valve after trap, and condensate return (return goes up about 10') as potential issues, and saw what I thought I should from the discharge based on what the trap manufacturer's say in their literature. No difference, tank temp still drops like a rock and never recovers. 180* to 140* in about 120 seconds, I am trying to maintain 160* minimum.

My next step was to do as you suggested, and I disconnected the pipe from the outlet of the coil, before the trap. At this point the coil was presumably full of condensate and when I called for heat I made sure I was well clear of the pipe as I expected that 22psi of steam and no trap would have cleared that condensate out of the coil very quickly and forcefully.

The result was not what I expected, and maybe I'm still not properly thinking like steam and envisioning this properly, but there was quite a delay any condensate came out, and at least (2) minutes before the condensate cleared completely, and I had steam flowing. Trouble is there was no way to know what pressure it was, it was just an open pipe ejecting steam into the room.

Again, thanks for your thoughts and response, there is always an answer and I will find it eventually, and I always appreciate a second brain to sort through these things. My major frustration is that I could do so many simple checks if this machine was not installed in the most unserviceable way possible. Trying to do as much troubleshooting as possible now, and then have a good plan when I return, we're going to need to schedule this for an overnight when the machine is down and I can remove lots of major components that will hopefully give me enough access to squeeze in and check what I need to.

unclejohn

If you get a chance to see David Byrne do, it new show is incredible. Other then that in sounds like you have a bad solenoid.

ScottSecor

Just a simple idea that may be an issue, is there any way for the condensate to drain after the solenoid closes? I suspect the the coil being filled with water in the beginning of a cycle is certainly not helping your warm up times (and really putting a strain on your coil from hammering).

findmyselfacity

unclejohn thanks! glad you know the reference, and I did actually manage to get tickets for the show around here in September before it sold out. Saw "Everything That Happens" show 5 times! Not sure where you're located, but there's a super great tribute band "Start Making Sense" that I see as often as I possibly can. Again tomorrow in fact. On a boat! Highly recommended. In regards to the situation at hand, I've grown increasingly suspicious of that solenoid valve as well, after all there's only so many possibilities and that's one of the ones I haven't been able to explore yet. I think I've finally got a plan formulated to get to it! Many thanks for the feedback.

findmyselfacity

Scott, hadn't thought about it that way, gives me something else to contemplate, I've also been wondering if there's a hairline crack or something in that coil... thanks

neilc

had an electric dw that stopped keeping temp,
coils amped out,
service tech finally asked if exhaust vents had been cleaned,
uuh YES,
and the cleaners left the dampers wide open and DW was ventilating way too much,
closed down outfeed damper all the way, and used infeed damper to control exhaust, and heat flow back into DW,
problem solved,
might be something to check.