4 replies to this topic

[shvet1]

Good day, forum

 

We have dosing positive-displacing pumps and PSVs located at pump discharge.  PSVs discharge back to pump suction. The problem is that pumps have variable suction pressure and I have an issue concerning PSV type and differential pressure. For example:

- PSV set pressure 10.5 barg

- normal suction pressure 3.5 barg

- max suction pressure 9.95 barg

 

I specified balanced bellows PSVs with such design that can assure variable superimposed backpressure does not affect set pressure. Vendor can not provide this and asked to approve constant superimposed backpressure 1.95 barg.

 

Dosign pumps are widely spread. Please comment - was I correct? Can a manufacturer porovide a balanced bellows spring PSV for a dosing pump with variable differential pressure? In case of my fault - please advice type of PSV. If this issue has been already discussed earlier please give a link.

Edited by shvet1, 28 March 2019 - 01:10 AM.

[breizh]

Hi ,

You may consider to talk to vendor like Pulsafeeder .

 

http://pulsatron.sal..._tech_sheet.pdf

 

Breizh 

[thorium90]

Why can the suction be normally 3.5Barg with max 9.95Barg (9.95 is suspiciously precise, but anyhow...)??

Isn't the suction connected to an atmospheric tank???

Or is the suction connected to a pressurized vessel with 3.5Barg normal operating pressure?

What are you dosing? Some oil, chemical, etc?

Edited by thorium90, 28 March 2019 - 08:17 AM.

[shvet1]

Why can the suction be normally 3.5Barg with max 9.95Barg (9.95 is suspiciously precise, but anyhow...)??

Isn't the suction connected to an atmospheric tank???

Or is the suction connected to a pressurized vessel with 3.5Barg normal operating pressure?

What are you dosing? Some oil, chemical, etc?

I am a detailed design Contractor. Licensor specified a positive-displacing pump for periodic pumping a chemical from a vessel (auto on/off). Vessel works with variable pressure 300-400 kPag. Vessel's PSV set pressure is 950 kPag. In pump datasheet Licensor specified max suction pressure 995 kPag (950 kPag SP + 45 kPag liquid height). Licensor specified design pressure of downstream equipment 1050 kPag and specified in pump datasheet that PSV set pressure equals 1050 kPag. 

As you can see I have nothing to do with this situation.

[samayaraj]

 

Why can the suction be normally 3.5Barg with max 9.95Barg (9.95 is suspiciously precise, but anyhow...)??

Isn't the suction connected to an atmospheric tank???

Or is the suction connected to a pressurized vessel with 3.5Barg normal operating pressure?

What are you dosing? Some oil, chemical, etc?

I am a detailed design Contractor. Licensor specified a positive-displacing pump for periodic pumping a chemical from a vessel (auto on/off). Vessel works with variable pressure 300-400 kPag. Vessel's PSV set pressure is 950 kPag. In pump datasheet Licensor specified max suction pressure 995 kPag (950 kPag SP + 45 kPag liquid height). Licensor specified design pressure of downstream equipment 1050 kPag and specified in pump datasheet that PSV set pressure equals 1050 kPag. 

As you can see I have nothing to do with this situation.

 

 

Im bit confused. You said operating pressure is 300-400 kPa(g). At what conditions vessel will reach set pressure of 950 kPa(g)?

 

Balanced bellow PSV can operate at back pressure up to 50 to 70% of set pressure. In your case the max. back pressure is near to design pressure of downstream equipment. So, you cannot use balanced bellow PSV.

 

I have few ideas for this situation:

 

1. Installing a pilot operated safety valve (Can be operated at various back pressure)

2. Installing a additional system with piping from downstream of PSV to vessel with lower back pressure. In this case, you can use conventional PSV. Later the process liquid from vessel can be transferred back to main vessel with separate pump.

Edited by samayaraj, 29 March 2019 - 02:55 AM.