Above ground tank dispenser problems...

[Zeke83]

I’ll try to be thorough as to not leave many questions, hopefully someone is familiar with our above ground tank set up. I am not an engineer but rather a mechanical tech, trying to resolve a problem with our above ground tank diesel dispensing set up. Our company engineers are clueless... We have two 9,900 gal. diesel tanks, arctic climate (-40 to 70 deg F year round) supply for the dispenser (gasboy 9153K) comes off the bottom of the tank to a manual gate valve, then to a butterfly valve with a solenoid that is dispenser controlled(actuates when dispenser pump is turned on/off) then to a Tokheim Model 52 pressure regulating valve, then the sheer valve and dispenser. Total length of piping is not long, maybe 30', 2" dia. i believe. The problems we are having are leakage from every gasketed surface of the pump and nozzle. Nozzles fail regularly, and most recently we had a spill from the dispenser pump air separator vent. After some research, i found that the Model 52 pressure regulating valve we have installed still has the blue shipping plug installed on the atmospheric vent (no vent line installed higher than tank level) This could definitely be the cause of the spill from the air separator vent line. My understanding of the air separator on the pump is incomplete at best. Initially i thought that the leakage problem was being caused by thermal expansion downstream of the PRV (dispenser side) which does contain an internal thermal relief for any pressure that builds UP stream of it, and is supposed to bleed through the pumps air separator vent line. In the trouble shooting section of the Model 52 PRV it clearly states that failure of the valves diaphragm or specifically not removing the blue shipping plug can cause release of fuel through the pumps air separator line, no mystery there. After researching this further though the mystery for me is why are we having so many leaks that initially I attributed to thermal expansion within the pump, not understanding that the pressure could vent itself downstream of the Model 52 PRV out the pumps air separator vent. Ambient temp for the past two months during this problem have been around -20 to 20 above F. Fuel from the tanks is at ambient, and the dispenser is enclosed and sometimes heated to around 80 deg. F. (some think that will fix our problem and I keep telling them it is making it worse!!) Any input would be greatly appreciated. I contacted the local vendor and their “expert” is out of state for a week. Thanks.

 

[LittleInch]

Definitely sounds like a thermal expansion issue to me. The volume increase won't be much but the pressure can be huge. Draw your system and consider whet you have locked in sections. Then either eliminate the locked in sections or install small relief valves with flow back to the tank or flow into the previous section until it ends up banc to the tank. You might also instal some small bladders which could absorb the small volume increase, but RVs are probably easier and better in the long run

You could try hoses instead of piping, but at -70 might find it difficult to get any.

I don't understand how the air separator can act aa RV. If it did you would be getting fuel out of the vent.

The only other issue is potentially surge preassure when you stop dispensing. What pressure relief system is built into the pump? If you're able to fit a pressure guages on the piping you can then see what happens during operation and static condition. This willgive you the data you really needs to see what is actually going on.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Zeke83]

The Model 52 PRV is a diaphragm design, specifically needed with above ground tanks to keep tank head pressure off the pump when not pumping. Tank head holds this valve closed until hydraulic suction pressure from the pump acts on the pilot valve and opens the diaphragm. When the pump shuts off and suction pressure is removed, spring pressure and tank head again close the valve. There is a small ball and spring check separate of the diaphragm that allows pressure to equalize from the downstream and upstream portion of the PRV that is integral to the PRV. This also allows any thermal expansion from upstream of the PRV (tank side) to bleed through... within the patent for the PRV which references specifically the Model 52 valve, it clearly explains that any thermal expansion pressure will bleed through this check and into the pump, and be allowed to dissipate the pressure by the expansion allowed by the pumps air separator vent... that is the grey area that I don’t know about, because I don’t know how the air separator on a fuel dispenser pump operates. My original thinking that the fuel inside the dispenser has nowhere to go was changed when I found the explanation of the internal pressure relief on the model 52 PRV. The model 52 PRV specifically states in the installation manual that thermal expansion reliefs must be installed when this valve is used... but makes no mention of the integral thermal relief already present within the valve. The PDF for the Model 52 is bellow..

 

[Zeke83]

http://www.veeder.com/gold/download.cfm?doc_id=1055

 

[LittleInch]

I've read the manual carefully and looked at the diagrams and can't see any reference to an integral relief valve, but two places where it says thermal relief valves are required in the piping system. In any event, this would only pass pressure through the valve to the d/s section. Air separators normally work by a float system which let's air out but then shuts off tight when liquid levels rise up so will provide no pressure relief.

If there are no pressure relief valves on the system then this is not good practice. You need to add some pressure gauges to check what's happening, but thermal relief valves would appear to be required.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Zeke83]

That’s that part that confuses me... the manufacture calls for thermal pressure relief(s) but, in fact, there is one on the valve itself. If you do a patent search in Google for patent number 5,143,258, pressure relief for vacuum operated valve, it specifically references this Tokheim Model 52, it says in no uncertain terms complete with diagrams "The fuel flowing through passage 52 (referencing the pressure relief within the valve itself, not the main diaphragm)is generally a very small amount and will pass into the air eliminator chamber (not shown) of the suction pump and thus be contained therein so that no fuel product is spilled on the ground."
Again, my lack of knowledge of how the suction pumps are separator functions is my hang up here... and your description would stand to reason that it would not function as a thermal expansion pressure relief as described through the air separator vent.
It seems that after the model 52 PRV it is pretty standard to have a shear valve, and then the dispenser intake piping... there is no space to plumb in a pressure relief, that would have to return the expanded fuel upstream of the solenoid operated tank valve.
At any rate after talking with our station engineer this morning, I am going to simply replace the Model 52 diaphragm, and install the vent for the diaphram that is supposed to be there anyway, instead of a 90 with the blue shipping plug in it. I will see what that solves if anything, I know for sure that will cure the spilling through the air separator vent, but not sure if it will have any effect on the thermal expansion leak problems. Thanks for your input littleinch.

http://www.google.com/patents/US5143258

 

[chicopee]

From your OP, it sounds like the space shuttle Challenger with gasket problems due to cold temperatures. You may want to talk to the manufacturer about the physical properties of the gaskets and compatibility with extreme cold temperatures. The gaskets may shrink, or harden and become brittle when very cold.After repeated fuelling procedures these gaskets break down.

 

[LittleInch]

Had a further look at the manual and there is a small thermal relief valve in the model 52 which is just not mentioned in the text (item 4 ). However it look like it pushes pressure forward so although there is little room downstream of the valve, you should definitely see if there is room for a trv between the solenoid valve and the prv. It also doesn't say what pressure the valve is set to.

Chicopee has a very valid point. Elastomers don't like low temps and the type 52 sheet quotes -13 to + 130F as its normal range.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[LittleInch]

An addiitonal point here now I've re-read all the above is that I actually can't work out how the PRV worked with a plug over the air vent. I can only assume it allowed some flow, some air crept past the plug, but the point then is that the model 52 would then not close until the air vented back through the plug which could be a few seconds or a few minutes. Either way all the downstream equipment would be subjected to surge presusres on shutting off the flow and other pressure it proably isn't designed for which the model 52 is supposed to stop.

Leakage through your air separator is either because the model 52 or some other componnet is letting in air which is them being forced out with some liquid through the air separator or your air separator seal is not functioning properly, posisbly due to the extreme low temp.

IMO you should fix the model 52 and its vent, install a thermal relief on the incoming line u/s the model 52 and check the temperature range of your elastomers in the system.

good luck

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way