6 replies to this topic

Hello,

I have a system where there is a tank which is 1m3 and i want to pump it to a head tank which is 20m above the tank. There is a vent line on the head tank which comes from the tank and is 3m long. The duty of the pump is 45m3/hr @ 35m. There is a line which leaves the head tank and goes on to heat a reactor.

I want to find out if the pump could pump the material out through the vent line.

How would i go about doing this?

Thanks

[Art Montemayor]

First of all, your problem description is very bad. Language is not your problem. You simply are not thinking or communicating your thoughts logically. It would be far better and more accurate for you to sketch out your system with all the dimensions on an Excel spreadsheet. If you don’t know how to draw in Excel look up the thread where I gave a small tutor workbook by using the SEARCH feature on this Forum.

Secondly, you don’t even state what TYPE of pump you are employing. If it is a positive displacement type, of course it will pump liquid up through the standpipe vent. If it is a centrifugal, it should be described by a performance curve. But please be specific and state what type of pump you are talking about. It makes all the difference in the world.

[JoeWong]

am1040,

Your posting has gained interest from Mr. Montemayor... If you can provide clear informations, you will get a very good and extraordinary response from him...Submit some sketch in Excel for better understanding...

pump head at least 35 m... the static head only 23 m... lookslike it can pass through the vent line and overflow...

Nevertheless, you did not specify pump type, motor rating, pressure drop, static different between pump and tank...

Hi Guys I have attached a excel spreadsheet of the problem.

Hopefully this makes it more clear.

Thanks

Attached Files

•  Head_tank.xls   16.5KB   126 downloads

[rsk]

You have not mentioned the pressure losses due to flow. As per specification of your pump its developed head is 35mwc. Suppose during flow

1.) Hs head loss through suction piping ie from head tank through reactor to pump suction.
2.) Hd head loss through discharge piping ie from pump through heating package to head tank .

Now Dynamic head at pump disharge=H= (30-Hs+35)m.
head availlable at inlet of vent tank=H-Hd-30-exit losses.

Hence if head availlable at inlet of tank is more than atmospheric pressure than water will flow out of vent line.

[Art Montemayor]

First of all, I want to clearly point out that this thread proves what I keep repeating: communicating accurately and logically is the first and most important responsibility of an engineer. If you don't do this, you mess everything and everybody up. Note how some of the respondents have "assumed" some things because they lack information or detail. In doing so, they make erroneous and mistaken comments. Also, note in my attached Workbook how a simple, detailed sketch shows up the lack of correct and proper information on the part of AM1040:

He fails to state clearly where in the dickens the flow is going to. Is it a closed, recirculation loop with the top tank acting as an expansion tank? Or is the flow going into the reactor where it has even more vapor space? I have shown by way of parallel piping and block valves how the flow can go to either of the two. That is why simply stating "There is a line which leaves the head tank and goes on to heat a reactor" is simply not enough information. An engineer should know this and state the correct, and accurate description. This is not about a language barrier; it's about the inability to use ones head in an intelligent and logical manner and subsequently communicate the information correctly and accurately.

Also note that unless AM1040 changes the scope and description, the system cannot overflow the top tank UNLESS there is excessive resistance in the line leaving the same top tank – which might cause the liquid to backup into the top tank and cause an overflow.

However, because of faulty and flawed information from AM1040, we cannot definitely state that the maximum developed head of the pump will cause the overflow. We simply have no information that clearly states that the pump head will exceed the height of the vent pipe. All AM1040 states is: "The duty of the pump is 45m3/hr @ 35m". That is NOT THE DUTY. That is a CAPACITY. It does not define the pump performance curve correctly. That is why I specifically requested the pump performance curve. In fact, we have no information from AM1040 that the pump is a CENTRIFUGAL PUMP.

All this pump seems to be doing is recirculating heating fluid. Therefore, sizing the discharge piping running from the top tank to the reactor is all that is needed to ensure that the vent doesn't overflow. It's that simple. However, we still don't have enough accurate, detailed information.

Because we don't have the above detailed and essential information, we can't make any deductions. All the respondents have done is GUESS. And that, gentlemen, IS NOT ENGINEERING!
 Head_tank_Rev1.xls   173KB   140 downloads

[fallah]

With fully accepting what Art stated as needed information to complete and clear the problem, let me state some minor comments:

-Because the head of circulating pumps usually consumed for frictional head of the total loop (not for providing static head) ,the head of pump specified by am1040 (35 m) looks like to be very high.

-Generally and theoretically, it might be said:the amount of pump head additional (if any) to the value needed for loop's frictional head,converts to static head above the normal level of the liquid in the head tank,provided that the sizes of the suction and discharge lines being the same or having no significant difference.Based on this statement,the possibility of overflowing from vent could be evaluated.