Piston vs Diaphragm metering Pump for Hcl and NaOH 2

[DjazAutomation]

Hello everybody,

I have to choose a Metering (dosing) pump for hydrochloric Acide (Hcl) at 30% and another one for Sodium Hydroxide (NaOH) at 30%.
Here are the specs:

For Hcl Pump:
- Maximum flow rate: 265 GPH (1000 liters/Hour)
- Head : 100 ft.

For NaOH Pump:
- maximum flow rate : 139 GPH (523 liters/Hour)
- Head : 100 ft.

I would like to know which metering pump technology (between daphragm and piston) is suitable for these applications.
Considering: Accuracy, Dry Run, Avoid Leakage (Hazardous fluids), Cost, maintenance, etc.

Thank you very much.

Djaz

 

[micalbrch]

I would definitely chose the diaphragm pump because it is hermetically sealed (the piston pump is not) and with these fluids leakages should not occur. Furthermore you have more choice concerning suitable wet end materials. Diaphragms are available in many different materials and so is the pump housing itself (plastic). Last but not least dry running is not a problem for a diaphragm pump but it is a problem for a piston pump.

About accuracy I assume it is more or less the same and so should be the maintenance costs. I think the initial costs are a little bit higher with a diaphragm pump but I'm not sure.

 

[DjazAutomation]

Thank you very much!

It seems that running with Diaphragm pumps can be safer than with piston pumps (Natural sealing). That's a critical important issue.

However, I am wondering how much would be the cost ratio between the two technologies consdering the same principal characteristics (Flow, Head, Materials).

When I think about the cost difference, i try to remember that piston pumps have been used for a long time for such applications and they are still in used. So it means that it can fit the application if we provide the good operation conditions (Flooded suction to not run dry, etc). What do you think? The problem for me is that i have to be competitive for a tender and the problem is that the client doesn't specify which metering pump technology he needs.

So, i am little be confusing for me and i don't want to compromise with safety.

Your kindly help is welcome.

Djaz



Thanks again

 

[micalbrch]

Get a quote for both options and then you will see what will be the cheaper solution. But specify the correct fluid data (temperature, concentrations) to be sure that the vendors can select suitable wet end materials.

 

[MJCronin]

All of you are not considering an important factor.

Air Operated Diaphragm pumps use a considerable amount of compressed air.

Operating costs are significant and may overtax an ancient existing aire system.

Has this compressed air demand been evaluated and have any air system improvements been incuded in the installed cost ?

-MJC

 

[micalbrch]

I hope he is not considering an AOD pump for metering applications as the flow of an AOD pump is not constant but depends upon the discharge pressure.

 

[DjazAutomation]

Thank you for your answers.
In fact, i am considering electrical motor driven dosing pumps.
I know now that a diaphragm pump cost is two to Four times the cost of a piston pump (I got a quote, thanks for the advice) with the same operating conditions. That's why i am wondering if i can consider the piston technology for my application.

One important thing is that my pumps will replace existing dosing pump (I couldn't find out the technology of the existing pumps since it's an old facillity and because the specs are lost, i attach the only drawing that i have and a photo of the existing dosing pumps, Maybe you can help me to recognise to which technology they belong. I think it's difficult to make a difference between a diaphragm and piston pump since they both look similar viewed from the outside)

Thank you for your kind help.

Djaz

 

[micalbrch]

That's a piston pump. Bertolini Pumps in Italy is the manufacturer. But I doubt that they still make the same models.

If such a pumps worked well so far, I'll won't switch to another more expensive technology.

 

[DjazAutomation]

Great!!!

Thank you all for your help and specially micalbrch.
As you said, I think it's better to keep the same technology (Piston) for this application as long as we garantee optimum operating conditions for this kind of pumps (Flooded suction, Safety Valve, good mainenance).

To be honest, i think that diaphragm pumps for this kind of applications (low pressure) are better than piston pumps because of their ability to run dry and to prevent (much better) hazardous leakage. I would say that if the cost was not so high, i would choose diaphragm pumps. However I would check their accuracy since i think they are less accurate (all things being relative) than piston pumps.

If i may, i have another question. What about pulsation dampeners that are installed at the discharge of dosing pumps (Piston pumps in my case)?
I keep in mind that they are sized according to the Strokes/minute of the piston, maximum flow rate and the design pressure of the process. Are they the only data to be taken into account for sizing a pulsation dampener? What else need to be considered?
Is there a link where i can get exauhstive method to size a pulsation dampener?

Having said that, there is an issue about Strokes/minute data given in the specs of a given piston pump:
Is one stroke considered as being a back and forth mouvement (Suction cycle + Discharge cycle)?
Or is it considered as being the discharge cycle only?
Or both the two mean the same?

Thank you all for you kind help. I really appreciate it.

Djaz

 

[micalbrch]

Djaz,

You need the stroke volume of the pump, the operating pressure and the kind of pump (simplex, duplex, triples etc.) and the allowable residual pulsation to determine the size of a pulsation dampener. Or you know the dampener size and the pump data and calculate what is the residual pulsation with the existing dampener. The stroke volume can of course be calculated if you have the flow rate and the stroke nos. on that flow rate. If you calculate the stroke volume by this, one "stroke" is a full stroke (suction plus discharge).

 

[DjazAutomation]

Thanks a lot micalbrch for all these valuable information.

That's an excellent idea to calculate the residual pulsation according to the existing installation (Dampener size, pump data). It's easy then to calculate the new dampener size according to the new dosing pump data.

Great!!

Djaz.