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another propane convention question on dual[ing] bulk tanks

Having established 10 lbs as the standard frst stage pressure (except maybe for blueberry processors who use 5 frequently) in a previous thread I'm on to the next convention. . .  speaking of conventions, just got back from the world of concrete in las vegas, but thus missed the chicago  show but I digress.

Have installed twin 1000 gallon tanks at our farm, mostly for storage capacity, but if the power went out on the coldest days of the year and the tanks were down to 10% full (gotta figure the murphy factor here)  then we would need the vaporization rate of both tanks to run the boiler and the generator at the same time.

So the industry standard to take advantage of vaporization from both tanks is to pipe the tanks together at tank pressure to a tee and then a common first stage regulator. The purpose here is to drain the tanks more or less evenly and take full advantage of the vaporization rate from both tanks.

On the other hand, the industry standard for single tanks is to mount the first stage regulator right under the tank cover and thus never have tank pressure running out from under the cover. vapor pressures aren't so crazy in the winter but they can stabilize at almost 200 lbs. in the summer.

So I'm trying to reason through what would happen if I put a first stage regulator on each tank and then tee them together.  The obvious problem that leads to use of a single regulator for both tanks is that no 2 regulators are going to be precisely identical in output pressure and you are going to tend to feed from one tank only or much more from one tank because one of the regulators will always be putting out a slightly higher pressure.

On the other hand, if I use two regulators and start to draw down one tank more than the other then the wetted surface will be reduced in that tank and its vaporization rate will slow.  my guess is that as long as the regulators are tuned reasonably close to one another that this lower vaporization rate coupled with the significant demand from the boiler would lower the delivery pressure enough to trigger delivery from the second regulator, thus see-sawing delivery of gas and somewhat evenly emptying the tanks.

This would allow for no tank pressure piping other than the 6" presto-lite whip to the regulator.

The simplest alternative if I'm going single regulator is prestolite by flare adapters and leading copper to a prestolite tee between the tanks that feeds the single regulator. The service pressures aren't any problem for that setup with a 3 times safety factor even for summer vapor pressures, and the only likely physical disturbance is when the tanks are filled and we deliberately located the feed several feet away and in back of the approach for the fill guy. So this means maybe a 6 foot run at tank pressure to the common regulator between the tanks which are about 3 feet apart.

But since i'm applying the murphy factor to the btu requirements, I reckon I could at least think of worst case scenarios, e.g. tree limb blowing into exposed copper piping and try to reason out whether I could regulate both tanks and keep the tank pressure confined under the covers.

Right now I'm just operating off a single tank at a time while I reckon the best approach here.





  • scott markle_2scott markle_2 Posts: 611Member
    natural feedback


    I'm not going to offer any opinions on the gas piping, but I think you are doing some good thinking in recognizing the possibility that "natural" feedback could effect the emptying of those tanks.
  • Plumdog_2Plumdog_2 Posts: 873Member
    LP Tank Farm

    I've piped a few "tank farms" where rows of four 1000 gal tanks were set side-by-side and level with each other. The vapor (top) ports were connected together with threaded steel , and the bottom (liquid) ports were also piped together, but in smaller diameter. Both sets of line led to an Evaporator, which had a burner heating a heavy vessel which would evaporate liquid LP returning it to the vapor manifolds. One large First-Stage reg took it from there. These "farms" needed to be a prescribed distance from occupied buildings, no trees allowed nearby, and the pipes more robustly supported than usual. You could probably connect your vapor ports together, then put a single reg on there. But use approved material for that job (probably not copper).  
  • TonySTonyS Posts: 849Member
    Here is a handy book I use

    Read the entire book, but look at the section on regulators and why 10 lbs should not be used in very cold weather.

    This should answer alot of your questions.

    Good Luck
  • lchmblchmb Posts: 2,941Member

    excess flow valve's in each tank. Pipe from each point to a regulator set between the two tanks and have a first stage regulator sized properly for the load. I use K copper (coated copper is acceptable also) and do not have any issues. btw, if you use black iron on tank pressure remember it needs to be schedule 80..

    Tony,  curious as to what your refering to about 10lb systems should not  be used in cold weather? I'll reread the regulator section tomorrow (brain is fried tonight)
  • lchmblchmb Posts: 2,941Member

    In localities where winter temperatures are extremely low, attention

    should be given to the setting of the first stage regulator to

    avoid the possibility of propane vapors recondensing into liquid

    in the line downstream of the first-stage regulator. For instance, if

    temperatures reach as low as -20ºF, the first-stage regulator should

    not be set higher than 10 psig. If temperatures reach as low as

    -35ºF, the setting of the first-stage regulator should not be higher

    than 5 psig.

    So if it's minus 35 in your area then I would follow this standard and drop your pressure to 5lbs...sorry I dont deal with temps that low so it's not something I consider...
  • TonySTonyS Posts: 849Member
    Liquid Draw

    You can also do a liquid draw and then vaporize in a heated area or device.

    This is how towmotors and larger generators are fed and then heat from the engine is used to vaporize the liquid. Tank size becomes inconsequential, except for duration.
  • archibald tuttlearchibald tuttle Posts: 632Member
    thanks for great suggestions and info


    I have used that book.  that is where i got my vaporization rates compared to tank fill and and tank dimensions and vapor pressures for tubing limits.  But i concede I haven't gone cover to cover and didn't see that caution against 10lbs regulators at extremely cold temps.

    That is maybe another explanation for why 5 lbs first stage regulators exist but you never seem to see them in our relatively temperate zone where we seldom get below 0.


    haven't seen those excess flow valves in use.  i guess I can just google to get the lowdown.  Makes a lot of sense. I was wondering if there was something like that.  That approach is prevalent for vulnerable water installations these days, e.g. washer hooks ups. So I used to stock "K" in a lot of coils but now my onhand stock is L or ACR (which is more or less L) I'm not sure what else the difference is other than maybe the tube is evaced and sealed before sale. Might be worth the extra edge here although I really like the excess flow approach if I'm piping tank pressure.

    so i'm not googling up anything that seems really aimed at my application in excess flow valves.  One rego list that came up was all 1" or bigger.  I'd be in 3/8", i.e 1/2 OD, tubing. From there it goes right down to grill style prestolites with 1/4" male connections.  I could jim crack that together, but POL to flare is the standard adapter I was going to use. 

    Also tyring to figure out the flow trip rate. a btu style chart would be handy.  I'm figuring maximum conceivable flow from each tank at about 500,000 BTU / hr.  I guess I can do some math to convert that to gallons and then check rates.  But if you have hooked these up, maybe you have a naufacturer and model line in mind so I have somewhere to start.

    Scott Markle and Everyone

    LAst question, while I think excess flow valve is probably the right murphy's law ingredient here, and standard protection for this kind of arrangement, I'm still musing on whether I would really experience wholly unpredictable or unsatisfactorily unbalanced delivery if I regulated at both tanks. Since I really hardly ever need the vaporizaiton rate of both tanks, I could give this a shot just to satisfy my curiosity.

    Anyone ever tried it or want to indulge my reasoning about what would happen in theory.


  • Mark EathertonMark Eatherton Posts: 5,843Member
    Tough to do.....

    Unless BOTH regulators are EXACTLY the same, the tanks will draw down independently.

    BTW, I am NOT an LP expert, but some of the basic hydraulics do still apply.

    My thinking is that if you have one common regulator after the raw tank pressures are tied together, your chances of achieving even draw down are excellent, assuming piping pressure drops are the same (avoid bull headed tees).

    I had a tank farm with 2 1000 gallon tanks, with individual primary regulators, both set for the same setting (+/_ 1/4 pound) and they never drew down equally. Once one tank was depleted, the other would kick in, which worked fine, but the owner wanted balanced draw down for some inane reason.

    Another option for increasing vaporization are band style tank heaters, which HR Rohr has discussed. Seems silly to use a more expensive energy (electricity) to increase the output of LP vapor, but it is proven to work in a pinch.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • LarryCLarryC Posts: 331Member
    Why not dual vapor regs and tie the liquids together?

    I am not a heating professional.

    Why can't you have the two vapor regulators with their outputs tied together and separately run a small line connecting the liquid ports of the tanks together? 

    Or, you could use each vapor regulator independantly for a load and and add a valve to tee them together.  Obviously with the liquid ports still tied together.

    That will give you two regulators to supply vapor and the cross tie will ensure both tanks are used equally.

    Obviously isolation valves will be needed for repair and maintenance.
  • lchmblchmb Posts: 2,941Member

    you use anything other than a pig/hogtail code requires that you install excess flow valve's on your tanks. As far as two regulator's, I have done that in cases with multiple loads and have no issue's doing it if there is a need. But if it's just a matter of storage, I dont see the need to install extra regulator's when not needed.
  • archibald tuttlearchibald tuttle Posts: 632Member
    edited January 2012
    the shipping from indonesia might be prohibitive

    but thanks much


    for beginning my search the correct excess flow valves.

    so this seems to be a link more aimed at the american market

    (page 54- and 55 of this catalog which is pages 58 and 59 of the underlying document.  it uses some kind of web reader but I assume its a .pdf)

    What I find from the indonesian link and from the victor catalog is that my btu rates are considered portable application. I'm figuring at approximately equal draw my max pull is a about 800,000 btu so thats 400,000 per tank.

    the lp service manual suggests a valve with 50% over anticipated max rate.  it doesn't say what temp to calc that at because these valves will pass much more gas at warmer temps. They offer a rating at 25 psi which is about 0 deg. F and a rating at 100 psi which is about 60 deg. F. Well it does get up to 90 here.

    Assuming that I should build 50% in at the lowest flow rate, the Victor/Webb 3199W closes at a rate of 265 SCHF (not sure why it isn't SCFH but I digress).  So the conversion I find for SCHF to btu is 2500, so that is 662,500 btus/hr flow at aroun 0 deg. F so that is about perfect, assuming I should be looking at flow at the lowest operating temp.

    That is a fitting designed for DOT cylinders. It's POL x 1/4 " male.

    It just seems odd to me that there isn't a relatively similar fitting designed for the permanent install market since the state of the art for a single tank is POL to Flare or POL to female pipe adapter. Female pipe would be a more useful format than male as the most common adapters are male pipe by  flare or you could simply proceed with pipe thread, but I would think some short copper whip would be appropriate given the geometry under the cover at the top of the tank, even if the rest of your crosspiping was steel.

    I can certainly use those webb fittings and I'll call my guy at webb to chase 'em up. But, maybe despite all this talk of linking tanks with K tube at tank pressure, etc., Mark's experience, i.e. regulator per tank and let them empty unevenly, is more common; and/or, dual tank equal draw installs are so uncommon that there isn't a dedicated line of hardware to the field service for residential propane for that application.


    got your idea which means more protection for the piping higher on the tanks.  Although they are in place and filled, and no provision was made for access to the liquid side so I'd have to empty them to install that.  And still would need excess flow valves as the liquid exit although I could probably bury a conduit between the tanks and there would be very little exposure for this liquid line to physical damage. but emptying the tanks is kind of the more daunting problem at the moment for implementing that approach. Should have researched this more before the tank drop.  The propane company was going to do the piping so I didn't double down on education when this started. But I get a certain dollar allowance which the salesman suggested would cover the install.  Then I had a friend who went through the process and got a whopping bill for overages so I got my plumber involved. He is in that boat of having pretty conversant knowledge of codes but hasn't done much propane work so he is not experienced with the frequent practices in the industry and he leaves the research to me because he is not too cyber involved and he knows I'm a retentive key puncher. (see previous thread on whether to choose 5 or 10 lbs. first stage).

    I'm fine on one tank at a time for the moment because the generator isn't even installed yet which is about a third of my anticipated maximum load and that means a single tank can vaporize what I'm running now even down to 0 deg. F without electric heaters. In a pinch that could make sense, but it does seem kind of silly to be spending electricity to free the btu's.

    Since the status can be quo for awhile, I remain interested in searching for a line of excess flow valves, if they exist, that is slightly better aimed at my application -- mostly from a connection standpoint. I believe, if my assumptions about the psi at which I should calculate the 50% excess flow that should trigger the valve are correct that the 265 SCHF is about right.

    Lastly, one I go to a single regulator dual tank setup,seems like a check tee would be sensible as well.  My only concern is, how much effective pipe length do I have to add to the calculations to determine that my btu delivery rate would be sufficient. I would imagine these Excess Flow Vales and Checks are going to have a noticeable effect on delivery under standard operating procedures.  I can't find any flo rating charts for tank pressure delivery to the 1st stage regulator although I can extrapolate from the rego's lp gas service manual that gives an adjustment factor for 20 psi delivery.  that is in the range of tank delivery pressure at the coldest temperatures I would experience. You add about 15% capacity to the 10 psi figures (actually they give a 15% deduction off your anticipated load).  So working that way, my heaviest anticipated load is 400,000 reduced by 15% that is 340,000 per tank.  3/8 OD is rated for 550,000 at 10 ft. My run is only about 6 feet to the common tee.  So maybe my plan to use 1/2 OD is even excessive.  Originally when I was looking at two regulators I was going to whip 5/8 OD that 7 feet to the common tee at 10 psi, but the pressure drop for that run would have to be added to the drop for the 100' of 1" PE underground feeder to the house regulator.

    The tables aren't very helpful with that because they don't really give you a method for calcing partial drops to add to the limit for two different diameters and pipe materials. They all assume a single run of a certain material.

    Anyway, I digress. How much do I need to add to my 6 feet either in 3/8" or 1/2" OD tubing (obviously the add equivalent would be different in each circumstance) for the Excess Flow and Check Tee.

    Another novel.

  • archibald tuttlearchibald tuttle Posts: 632Member
    resetting excess flow valves

    BTW, I'm sure when I get one it might say in the literature but given my cursing of Ralph Nader types when the excess flow valve on my grill locks out because the grill was on when I opened the tank, what is the reset protocol for these. I would guess if you equalize the pressure on the downstream side, that would do it, but how do you equalize the pressure without propane flowing . . .?

    Speaking of which, has anybody tried to use one of those EPA approved gas cans lately.  no wonder there is a black market in the old spouts that sell for more than the cost of one of the new containers . . . our government at work trying to make work as difficult as possible for those with a real job.

  • LarryCLarryC Posts: 331Member
    Equalizing pressure around excess flow valves.


    In my dark distant nuclear past, we used small bypass valves around the large isolations valves to equalize pressures to allow the opening of the larger valves.  We opened a small passage, let the fluid flow until the pressure differential was small enough, opened the large valve and then shut the bypass.  The bypass valves were always shut except when in use.

      I am ASSuming there is a similar feature that permits you to do the same.
  • lchmblchmb Posts: 2,941Member

    didnt look at the link just looked at the picture. I have some POL to 1/2" ips excess valves in the shop and will get the gallon rating on them tomorrow. For 800k I would run 1/2 coated copper, and if your really worried, come off each valve with copper and transition to 1/2 sched 80 black iron. Then you can run black iron between the tanks and create a stand for your first stage regulator to mount to. I generally mount the piping up on to the tanks and use beam hanger's to secure it to the lifting lug on each tank..

     If the excess flow valve locks out you simply close your delivery valve and wait for it to reset. Once done open your valve slowly to refill the line (you would of course correct the issue that caused it to close in the first place).

    I would not run underground liquid lines, due to code requirements...and really you have no need at that btu load....
  • archibald tuttlearchibald tuttle Posts: 632Member
    hijacking my own thread - gas cocks versus ball valves

    is it really threadjacking if I see the question as following?

    I was trying to figure out what standard of valves to use in these setups on first and second stages. I had decided on standard full port ball valves on the first stage side given the pressure is higher than ordinarily seen by gas cocks although I don't see any pressure ratings on any the gas cocks I've got in stock, but it got me thinking that there isn't that much of a discount these days for a gas cock compared to a standard ball valve.

    in terms of design appropriateness, I used to thing the old brass on brass tapered cylinder and receiver made some sense since it was so easier to tighten if you ever bubbled a tiny bit on a valve.

    While it is hard to conceive of a standard ball valve seeping at the stuffing box on such low pressures, esp. on the secondary side, I'm just wondering if there might be any design considerations in contemporary gas cocks that aren't obvious to my eye but that conceivably promise a longer service life at these lower pressures or if it is all about shaving 20% in cost but you aren't improving your performance and/or are conceivably adopting a less robust platform.

    My wholesaler says that although he sells the gas cocks and they are about 20% cheaper in any given size, the industry is moving to standard ball valves on gas. Any reason I shouldn't move with the industry?

    and lchmb, did you get any specs/model #s on your POL by 1/2" IPS (male or female?) excess flow valves?


  • lchmblchmb Posts: 2,941Member
    edited February 2012

    for the delay...been a busy's a link to some. You will need to know your total load and then have your supplier size the excess flow valve for you. What area are you located in? Not sure I saw it posted....

    In reference to the shutoffs..I only use valves rated for 300lbs w.o.g. Probably more expensive but you generally get what you pay for...
  • PeterNHPeterNH Posts: 88Member

    Hello Brian,

    In the restaurant i used to own we had two 1000 gallon tanks.

    There were piped (vapor?) together with iron pipe. Then there was a primary regulator.  Iron pipe in the ground led to the building where there was another, secondary regulator.  This connected to a 3 inch cast iron main that ran the whole length of the kitchen. About 70 feet.

    Tee's of various sizes came of the main to a plethora of equipment and 2 bsmall boilers.

    Back in the later 80's thing s were really "cookin'"

    two 60k boilers.

    two big pressure less steamers.

    360k  water heater

    100k hobart infared booster.

    3 convetion ovens

    overfired South Bend broiler.

    4 big ranges

    3 ovens under the ranges

    small fryer

    a stock pot range, 2 giant burners, maybe 60k+ each?

    There was more than one New Year's eve when everything was running and it was down near zero or below outside.

    And lot's of Saturay nights when it was -10 to -20 out with say 70% of everything running.

    For sure there is at least 1,200,000 btu's

    Never had a problem with the gas.

    No matter how cold it got.

    We only got one ticket for the tank fills, but it would seem that it took about the same amount of time to fill each tank.

    Hope this helps,

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