14 replies to this topic

[kangas]

If the max head of a diaphragm pump is 80m (8bar) does it mean that the line needs to be designed at 8bar?

 

Boxer 15 - Debem

Edited by kangas, 08 April 2022 - 09:35 AM.

[Pilesar]

As a rule, the design pressure for every component in the system should be at or above the most severe condition the component is expected to experience. The system evaluation requires more information than just knowing the maximum pump head.

[fallah]

If the max head of a diaphragm pump is 80m (8bar) does it mean that the line needs to be designed at 8bar?

 

 

Hi,

 

In general, yes, the pump discharge pressure should be designed at 8 barg...but to get a better and more accurate response it's needed more info including the relevant process description, system hydraulic, PID/Sketch,...

[latexman]

Most pipe and fittings are purchased at standard thicknesses, like Schedule 10, 40, and 80.  Rarely is pipe designed and made to a specific thickness in a special mill run, except in the case of long pipeline projects.  This is how pipe economics have been for many, many decades.

 

So, most engineers do not design pipe and fittings to a specific pressure.  They usually select a "pipe spec" that already exists in the plant/business/company whose design limits and materials of construction exceed the requirements of their line.

 

Can you imagine the huge supply chain and logistic issues in a plant if every line was designed to a specific, different pressure?  It would be crippling!  Thus, we have purchasing standards and pipe specs.

 

Usually AODD pumps are for relatively short runs of pipe, compared to pipelines that are km's long.  So, I'm guessing it will be optimum for you to select standard thickness pipe, and hopefully there are existing pipe specs for you to pick from.

 

After your line is constructed the contractor will ask, what pressure do we test this line at?  Almost always, I request the line be tested to the limit of that size line in the pipe spec.  Otherwise, one is leaving money on the table, and one day in the future that line may be repurposed for higher pressure than 8 barg.

[Art Montemayor]

I fully agree with Latex's response and advice.  To me, it represents the essence of knowledge and - most importantly - field experience.  As Latex points out, many engineering tools and answers are based on common sense - in other words, many times high math and complicated equations are not part of the safe, simple, and efficient answer.  To help you answer the basic question you raise in factual data and numbers, please see the attached documents.

 

I hope they help you out and allow you to feel safe and secure with all the piping around you and not having to make all these tedious calculations every time you have to apply a piping installation.

 

Note: to accentuate how much protection you inherently have in common schedule 40 plant piping, I've high-lighted the common sizes.  Not many processes have to work in the 1,000 psi+ range.

 

 Pipe Pressure Rating.pdf   1.42MB   103 downloads

 Pipe Strength Calculations.docx   59.09KB   68 downloads

[kangas]

Thanks for the advice. So I guess for 8 bar I shouldn't worry if I take a schedule40 pipe.

[latexman]

Consult the selected pipe spec.  The limits should be in there.

[puval]

Thank you Admins and members for the detailed explanations. I would like to add a general point of positive displacement pump.

Since the discharge pressure depends on downstream system and relief valve setting in positive displacement pump system, i think this also needs to be accounted in deciding the max. system pressure.

Please correct me.

Edited by puval, 12 April 2022 - 01:02 PM.

[Art Montemayor]

Puval:

 

Your comment tends to be confusing due to the fact that the original poster (OP) already gave us the Basic Data.  He stated: “If the max head of a diaphragm pump is 80 m (8bar) does it mean that the line needs to be designed at 8 bar?”

 

The OP has already stated what the maximum discharge pressure of the pump is.  He stated that it is 8 bar.  In other words, this thread is about selecting the appropriate pipe specifications that will safely take 8 bar.  Latexman answered this query in a very detailed and accurate manner.

 

I believe you mean to interject that the OP should take other factors – like the relief valve setting(s) – into consideration.  I believe this issue has already been addressed indirectly by Latexman.  My opinion is that the OP’s direct query has been addressed and answered.  However, the OP never has identified other items that are subjected to the pump’s discharge pressure – such as valves, fittings, hoses, instruments, etc., etc.  All these factors have to be addressed and subjected to the plant’s pipe specifications – as indicated by Latexman.  It has to be assumed that the OP (and all readers) realize that it is common sense to take into consideration ALL items in the discharge line - not just one component.

[puval]

My apologies for the confusion Art Montemayor. My intention was to give additional background on arriving max. pressure. But did not expect ending up in confusion.

Thank you

[kangas]

Do I need to have a relief line on a positive displacement? I am handling dangerous chemicals.

[fallah]

Do I need to have a relief line on a positive displacement? I am handling dangerous chemicals.

 

Hi,

 

For its relevant PRV on discharge line, yes...

[latexman]

Do I need to have a relief line on a positive displacement? I am handling dangerous chemicals.

 

Your link in the original post is an AODD pump.  Those type PD pumps "stall" (stop pumping) when the pump discharge pressure = the supply air pressure.  So if the normal air supply pressure < the design pressure of the line, no PSV is needed.  It is inherently safe by design.

 

In our plants, air compressors start at 80 psig and stop at 100 psig.  We use a galvanized  CS 125 psi class pipe spec (which is good for up to 150 psig for pipe < 24" NPS up to 150^oF).  So, we do not put PSV's downstream of our AODD pumps.  It is inherently safe by design.

 

If your pump is not a AODD pump, you might need a PSV, but we have no info. on that unless you tell us more.

[breizh]

Hi,

What chemical are you talking about ?

Did you check the compatibility of this chemical with your pump ? 

Breizh 

[kangas]

Hi,

What chemical are you talking about ?

Did you check the compatibility of this chemical with your pump ? 

Breizh 

Breizh, 

 

the chemicals to transfer is acetyl chloride.

Yes pump is compatible.