LPG Pump Suction and Tank Levels

• Arrange for the tanks to be geometrically equidistant from a common point. Arrange for the pipelines to that point to be the same diameter. Take the suction of the pump from the common point, or
• one could reduce the flowrate passing through the pump until the level difference is immeasurable, or
• one could replace the four tanks with one tank four times the volume, or
• one could put a partly-open valve in the line from tank 4

Thank you PWSlack,

Point 4: partly open valve on tank 4 sounds like an ideal solution for me.

Best Regards

The surest way is to make the piping symmetrical, especially the pump suction, but maybe also the by-pass line, probably not the vapor line. But first, all tanks are identical and installed at the same elevation, correct?

To make the piping symmetrical, pipe from 1 to 2 and from 3 to 4. In the center of each of these 2 lines, install a 'T' and then run a line between the 2 'T's. In the center of this line install a 'T' and run from here to the pump suction. In the first 3 lines, it is imperative that the lines be mirror images on both sides of the 'T', i.e. if it takes 2 elbows to get out of tank 1, make sure there are 2 elbows at the other 3 tanks as well. When you get through, you can follow the flow path from each tank to the pump and each path should go through the same number of fittings and the same length of pipe.

If a fitting is required on the piping to the pump is required, it is advisable to have 5 to 10 pipe diameters of straight pipe between the 'T' and the other fitting. This may not be clear. If not, can you post a picture of the installation?

Thanks Bigg,

I think you hit the nail on the head. Our design should have been as how your described it. PWSlack suggested for a partly open valve on tank 4 which I will use as my short term fix untill we modify the pipe work as above( long term fix).

Super

Thanks Bigg,

I think you hit the nail on the head. Our design should have been as how you described it. PWSlack suggested a partly open valve on tank 4 which I will use as a short term fix untill we modify the pipework to have a tee and suction coming from the center of all four tanks.

Super

yes, post a picture of the installation...

Hi yesyen,

A timely reminder.

Thanks

Hi Why worry about it?? IF you are getting enough fuel from the setup and you clearly know how much fuel you have then why even worry about it?? Your Assumption is correct in that the 4th tank is closer to the pump thus gets drained a little faster. IF you were drawing off Vapor rather than LP it could be a problem as the tank would ice up. But as long as you get enough fuel even if tank 4 runs dry I would just not even go to the trouble of redoing the system. In Short. If it works. Do not worry about it.

However. If for some reason not mentioned this is a problem then use larger pipe from the other 3 tanks. Even with the Vapor Crossover to keep the pressure the same in all tanks the problem is simply a law of force. It is easyer to flow from tank 4 than the other tanks. But a Larger Pipe will help and also hook a pipe to tank 1 to the pump via a T joint just before the pump and at the pipe. But this will only cause tank 1 and 4 to drain faster than 2 and 3 as the flow from what ever is closer to the pump as far as flow goes rather than distance is realy the cause because as it is now tank 4 the fuel hits the drain pipe at a 90 degree angle and causes a higher pressure area cutting flow from the others until it gets lower on fule. There are many ways to fix the issue and I give some below.

Another way is to build a manafold. Pretty much what you have with your current pipeing system. But have all 4 tanks go to One Larger pipe and hook to the Larger pipe that will be the manafold at a 90 degree angle from the 4 incoming pipes. Make this larger pipe long and at least 5 times the size of the incoming pipes. Why do this. because of what is causing the problem in the first place that I do not see as a problem based on Data given but if it is a problem then this will fix the issue as you will not have the flow comming into the current pipe from tank 4 causes a higher pressure in that part of the pipe thus blocking off the flow from the others. This also tells us that you are using a lot of fuel when the thing is running. Anyway I hope all is working for you and you can just say leave it alone. Why do all tanks have to be the same level??? Think about it. Also when the shift is done the tanks will almost level out to the same. Not all the way but close. So I would say Just leave it alone.

Jim

Hi Jimmyjoejetter,

Thanks mate for shooting from a different angle. It opened me up

Best Regards

Hello Anon,

This really must be a homework question eh?

Considering an operational pumped LPG system,your questions would have all been answered & addressed by the installers & engineers leaving your pump to be concerned with.

That said,either your pump is failing or simply lost a phase resulting in reduced pumping performance.

As for your homework,basic pumping design considerations should be applied.

HTH

Jay

Hi Mr Fixit,

No, it is a real life challenge. A lesson I guess to ensure the dos & don't of pump installation is discused with the manufacturers prior to installation.

Best Regards

The difference between 5% and 70% is too high to be attributed to just pipe length or proximity!

Your problem is due to the fact that some vapor will become present in the interconnecting pipes, and will be drawn to the connection nearest the pump. This will cause a kind of vapor lock that will prevent the 3 back tanks from delivering liquid as should be normally. Tank 4 will be draining to the pump at much higher rate!

Solution: you need to slope the pipes down from tank 1 to 2, to 3 and to 4 (Lowest point before pump suction entry). This way, any Vapor formation will be going back to the end of the pipe, towards tank1 and, there, have an extra pipe going back and Up to the top of tank1, to the vapor zone. This will allow tank1 to drain evenly, like the others

The most important issue is to prevent the vapor from sloping upward towards the pump suction! If the system was working fine for some time before exhibiting this problem, and this just happened recently or does happen from time to time, then the pipe slope is either zero or just slightly upward to the pump, or something just happened to sag it this way. Check and good luck

Hi LAA Lucke,

Your analysis is good. Consolidating the responses from all I think I have found myself a short term and a long term fix + other design considerations that will prove useful in future.

Best Regards

Restricting valve on tank 4 might not work if the problem is a Vapor trap in the pipes.

You might experience the same problem on another tank (Maybe nr 3 this time). or loss of priming whereby no fluid in the pump!

Check the pipe work installation to see if there is any high point where Vapor can get traped, thus preventing flow from the 3 tanks, in favor for tank 4. Might be between Nr 3 and Nr 4.

Balancing the flows from the different tanks by patial closure of the valves would have been suggested if the liquid levels in the tanks were gradually decreasing from Nr 1 to Nr 4. You said that 1, 2 & 3 were 75% full when 4 was only 5% full. This points to a possible block between 3 and 4, and this blockage can be a vapor trap if nothing else (like restriction in pipe or some foreign matter ...