Hermetic pumps » suction line

[Sandro Baptista]

file:///C:/TEMP/moz-screenshot-3.pngfile:///C:/TEMP/moz-screenshot-4.pngDoes anybody know the reasons for this?

[Josip]

Hi, Sandro Baptista :)


file:///C:/TEMP/moz-screenshot-3.pngfile:///C:/TEMP/moz-screenshot-4.pngDoes anybody know the reasons for this?

if both pumps are running in the same time they can create lower pressure at suction down-leg what can cause cavitation ... in case with 3 or more pumps (one or two as standby) the best is to make separate suction pipes for each pump .... check valve on each discharge pipe connected to common header...


please, search RE forum regarding cavitation, refrigerant pumps etc... ;) you must find a lot of posts... enough to read next two days..;)

Best regards, Josip :)

[RANGER1]

Sandro,
I think they are advising this for a few reasons.

Also in their handbook they also refer to liquid flow in m/sec in suction line to pump.

This is so there is no restriction or pressure drop to pump.

Also to reduce possibility of suction line of pump having any ambient heat gain (possibly causing gas bubbles & cavitation) if suction line is to long or to small flow through it.

Any horizontal pipe runs in suction to pump should also sloped upwards to vessel suction to allow any gas bubbles escape in idle period.

[Sandro Baptista]

Hi, Sandro Baptista :)
if both pumps are running in the same time they can create lower pressure at suction down-leg what can cause cavitation ... in case with 3 or more pumps (one or two as standby) the best is to make separate suction pipes for each pump .... check valve on each discharge pipe connected to common header...




But you can dimension the down-leg cross section to flow the liquid refrigerant corresponding to the two pumps working at the same time with low velocity.

[Sandro Baptista]

Sandro,
I think they are advising this for a few reasons.


Also to reduce possibility of suction line of pump having any ambient heat gain (possibly causing gas bubbles & cavitation) if suction line is to long or to small flow through it.


Ranger, grabbing in what you have said if there is a common down-leg then the suction line to the pump will be cold as soon one pump is working so less prone to bubble & cavitation, as you have said. However even if there is individual down-leg with a good design that effect will not have any negative impact.

[Sandro Baptista]

I'd like to listen more opinions from the REF guys about these subject.

As I said previous I still don't see why should we have one down-leg for each active pump if the down-leg been sized to guarantee a low velocity when all pumps are working.

Waiting you comments.

[Josip]

Hi, Sandro :)

But you can dimension the down-leg cross section to flow the liquid refrigerant corresponding to the two pumps working at the same time with low velocity.


We can do what we want ;), but ...

Try to calculate the cost of one separator with 4 separate pipes for 4 pumps (3 are running and one is standby) ... for example each pipe should be 6" (to connect pumps separately) ... and

try to calculate the cost of the same separator with down-leg for the same 4 pumps .... including ...

transportation problems ... vortex brake plates inside of down-leg pipe, installation and welding of down-leg on site, x-ray of welding or someone can prefer big flanges with gasket and big 24/36 bolts, additional supports ... etc ... quite big practical problems ...

... but the best is to search RE forums for ... liquid overfeed, ammonia pumps, hermetic pumps ..etc ... a lot to read from many other RE members ... then we can discuss this again if you like ....


Best regards, Josip :)

[Sandro Baptista]

4" to a one pump is already a good leg to a great capacity.

[Josip]

Hi, Sandro :)


4" to a one pump is already a good leg to a great capacity.

agree with you - but depend what for we are using our pump to feed ... air coolers, plate freezers or liquid chillers ...

6" pipe for down-leg was an example only...



But you can dimension the down-leg cross section to flow the liquid refrigerant corresponding to the two pumps working at the same time with low velocity.

... how many m/s you assume as low velocity in down-leg?


Best regards, Josip :)

[Sandro Baptista]

Hi, Sandro :)
... how many m/s you assume as low velocity in down-leg?
Best regards, Josip :)

less than 0,5 m/s it's low velocity in down-leg, specially for a big nominal diameter pipe. Don't you agree. A 4" pipe tube allows a great capacity for a recirculating factors like n=2,4 or 6.

The "pumps interference" that is mentioned on sketch you send maybe is about bubbles or even worst if one of them cavitate for any reason?

[Josip]

Hi, Sandro :)


less than 0,5 m/s it's low velocity in down-leg, specially for a big nominal diameter pipe. Don't you agree. A 4" pipe tube allows a great capacity for a recirculating factors like n=2,4 or 6.

The "pumps interference" that is mentioned on sketch you send maybe is about bubbles or even worst if one of them cavitate for any reason?

velocity should be less then o,3 m/s in the down-leg for ammonia plant ...

in case of sudden change of pressure within separator gas bubbles first go up - rise due to evaporation ... if we have higher velocity then gas bubbles change direction and go down into pump causing cavitation ....

.... "pumps interference" when pumps are working parallel .. means one pump is "stealing" liquid from another causing evaporation of refrigerant thus bubble "production" what again is leading into cavitation of one or both pumps ...

For that reason it is very important design of down-leg and determination of the correct internal diameter...


Best regards, Josip :)

[Sandro Baptista]

Sorry the persistence Josip.

Still can understand quite well what you have said on your last post.

Grab the pdf "hermetic pumps installation one pump is stand by". Now imagine that down-leg ensure low velocity (Hermetic says between 0,3 and 0,5 m/s) with the 2 pumps working at the same time (my opinion is that works like a mirror with a pump on each side and the fluid stream lines are symmetrical)...okay you say that is a trouble according with your arguments.
Now imagine that you replace those 2 pumps by just one with the double flow of the each others...Now the system would work well?...I guess so.

I may look crazy but in fact my opinion is that if there is one pump in stand by this one should have an independent down-leg because in this way less oil will be carry to pump suction and accumulate there. With the same down-leg using the 2 pumps (with one one stand by) the one that is off must once in a while work a little to discharge out the oil. On the another way I believe that problem could happen but is less meaningful.

[Josip]

Hi, Sandro :)


Sorry the persistence Josip.

Still can understand quite well what you have said on your last post.

Grab the pdf "hermetic pumps installation one pump is stand by". Now imagine that down-leg ensure low velocity (Hermetic says between 0,3 and 0,5 m/s) with the 2 pumps working at the same time (my opinion is that works like a mirror with a pump on each side and the fluid stream lines are symmetrical)...okay you say that is a trouble according with your arguments.
Now imagine that you replace those 2 pumps by just one with the double flow of the each others...Now the system would work well?...I guess so.


No, problem this is discussion (in English language, sometimes is not easy to explain what I want to say) and we are speaking about something what is sometimes in gray zone;)

With two pumps connected to a common down-leg can be a lot of problems, believe me I was there;)

If we replace two pumps with only one we have to be sure that our down leg is designed and sized for capacity of that one pump...




I may look crazy but in fact my opinion is that if there is one pump in stand by this one should have an independent down-leg because in this way less oil will be carry to pump suction and accumulate there. With the same down-leg using the 2 pumps (with one one stand by) the one that is off must once in a while work a little to discharge out the oil. On the another way I believe that problem could happen but is less meaningful.

Regarding connection of two separate pumps to separator figure 8 is not correct ... we have to use the same design of down-leg as for two pumps with one as stand by, like on figure 9 ... down-leg must protrude into separator for 30-40mm and if down-leg is bigger we need vortex breaker see attached document...

Of course, we have to assure lead/lag work of pumps every 2-3 days, but if we have a lot of oil within ammonia it is much better to change pumps daily...


Best regards, Josip :)

[Sandro Baptista]

Hi, Sandro :)




No, problem this is discussion (in English language, sometimes is not easy to explain what I want to say) and we are speaking about something what is sometimes in gray zone;)

With two pumps connected to a common down-leg can be a lot of problems, believe me I was there;)

If we replace two pumps with only one we have to be sure that our down leg is designed and sized for capacity of that one pump...




Regarding connection of two separate pumps to separator figure 8 is not correct ... we have to use the same design of down-leg as for two pumps with one as stand by, like on figure 9 ... down-leg must protrude into separator for 30-40mm and if down-leg is bigger we need vortex breaker see attached document...

Of course, we have to assure lead/lag work of pumps every 2-3 days, but if we have a lot of oil within ammonia it is much better to change pumps daily...


Best regards, Josip :)

Josip,

I understand your english very well.

About have 1 independent leg for the stand by pump because of the prone of getting more oil if the leg is shared with de stand by pump: do you agree or not?

BR

[Josip]

Hi, Sandro :)


Josip,

I understand your english very well.

About have 1 independent leg for the stand by pump because of the prone of getting more oil if the leg is shared with de stand by pump: do you agree or not?

BR

Sorry, do not catch this one ...

Best regards, Josip :)

[michaelm]

B”H

Josip,
How to obtain the full Manual for the pump installation. Kind regards.

[Josip]

Hi, michaelm :)




B”H


Josip,
How to obtain the full Manual for the pump installation. Kind regards.

I believe here on RE forums you can find a lot of links to a different documents regarding refrigeration pumps...

here is one link ...

http://http://www.hermetic-pumpen.com/en/hermetic/industries/refrigeration-industry/installation-note.html (http://http//www.hermetic-pumpen.com/en/hermetic/industries/refrigeration-industry/installation-note.html)

you can try Google .... hermetic pumps installation..


Best regards, Josip :)

[Sandro Baptista]

Hi, Sandro :)
"About have 1 independent leg for the stand by pump because of the prone of getting more oil if the leg is shared with de stand by pump: do you agree or not?"



Sorry, do not catch this one ...

Best regards, Josip :)

okay, no problem :)

Do you agree or nor that would be better the stand by pump be connected to an individual down-leg so it don't get so much oil accumulated while is idle.

[Josip]

Hi, Sandro :)


okay, no problem :)

Do you agree or nor that would be better the stand by pump be connected to an individual down-leg so it don't get so much oil accumulated while is idle.

If we have two pumps and one is standby I'll use only one down-leg with proper design ... diameter, length, vortex breaker, oil drain etc ... in my opinion no need for two separate down-legs ....

separate down-legs I'll use only at separator with three or more pumps...

Best regards, Josip :)

[Sandro Baptista]

Hi, Sandro :)



If we have two pumps and one is standby I'll use only one down-leg with proper design ... diameter, length, vortex breaker, oil drain etc ... in my opinion no need for two separate down-legs ....

separate down-legs I'll use only at separator with three or more pumps...

Best regards, Josip :)

But when the active pump is sucking liquid this liquid will bring oil and I see that part of this oil going on (by gravity) to the stand by pump.

[Josip]

Hi, Sandro :)


But when the active pump is sucking liquid this liquid will bring oil and I see that part of this oil going on (by gravity) to the stand by pump.

please, check post #13 again regarding lead/lag of pumps to avoid oil problems at the bottom of down-leg (figure 9) can be installed oil draining valve or each pump can be equipped with oil drain valve ...

... but, let me ask you something ... why do you worry so much about oil ... is your plant an old plant where you installed new hermetic pumps and you faced problems with oil or something else?

if you have so much oil within separator or system, there must be some other cause for that ... bad oil separators, wrong type of oil, not regularly draining of oil etc...

Best regards, Josip :)

[Sandro Baptista]

Hi, Sandro :)

please, check post #13 again regarding lead/lag of pumps to avoid oil problems at the bottom of down-leg (figure 9) can be installed oil draining valve or each pump can be equipped with oil drain valve ...

... but, let me ask you something ... why do you worry so much about oil ... is your plant an old plant where you installed new hermetic pumps and you faced problems with oil or something else?

if you have so much oil within separator or system, there must be some other cause for that ... bad oil separators, wrong type of oil, not regularly draining of oil etc...

Best regards, Josip :)

Hello Josip,

1) I have no problem with any plant about oil in the pumps

2) We use to supply one down leg for each pump, even for the one that is in stand by

3) We have old refrigerant plant with 2 pumps working at the same time and with the same down-leg, though at the beginning the design was only for one pump working. But after a few years the client wanted to extend the plant and we had to put the second pump ON. The plant is working fine.

Regards

[michaelm]

B”H
Josip,
I was referring to the Manual that you posted some pictures from for Sandro.
What manual is that?
Kind regards.

[Josip]

Hi, Sandro :)


Hello Josip,

1) I have no problem with any plant about oil in the pumps

2) We use to supply one down leg for each pump, even for the one that is in stand by

3) We have old refrigerant plant with 2 pumps working at the same time and with the same down-leg, though at the beginning the design was only for one pump working. But after a few years the client wanted to extend the plant and we had to put the second pump ON. The plant is working fine.

Regards

Good, very good ...

Best regards, Josip :)

[Josip]

Hi, michaelm :)




B”H

Josip,
I was referring to the Manual that you posted some pictures from for Sandro.
What manual is that?
Kind regards.



some instructions how to install hermetic pumps, sorry, cannot help too much ... have only some hard copy pages, but without any data about author&publisher ...


Best regards, Josip :)