13 replies to this topic

[Rahimzadeh]

Dears:
Rotation speed of horizental centrifugal pump must greater than vertical pump?

Please tell me preferred RPM for single or multi stage vertical pumps?

Best regards

M.R.Rahimzadeh

[Art Montemayor]

<sup>M.R.Rahimzadeh:

The speed of a centrifugal pump is mainly determined by the type of DRIVER it has connected to it. This is pretty obvious, but you fail to state how you are driving the centifugal pump in your query.

If your driver is an electric motor, your first question has the answer of: both vertical and horizontal pumps are subjected to the same, set motor speeds. There are high-speed pumps with geared drives (such as Sundyne), but these are the exception.

Again, if you have an electric motor drive, single or multi stage vertical pumps are driven at the set speeds of the electric motor. Your electric motor has set speeds that depend on the frequency of the fed electric current and number of poles of the motor. Again, this is pretty basic stuff.

If you have a steam or gas driven pump, then you have variable speed available for the pump, so your questions have no relationship to this type of drive.

What type of driver are you contemplating for the subject centrifugal pump?</sup>

[Rahimzadeh]

Thanks Mr. Artemontemayor:
My mean from this question is that multi stage vertical pump is more vulnerable than centrifugal pump or not?

In some standard thar recommend the users prefer lower speed electromotor.
Thanks

[kkala]

Comparison of vertical versus horizontal centrifugal pumps has been in http://www.cheresources.com/invision/topic/4290-horizontal-vs-vertical-centrifugal-pump/, http://www.cheresources.com/invision/topic/13367-vertical-can-type-pump, http://centrifugalpump.org/pump_horizontal_vertical.html, but no note has been traced about the rotational speed (RPM).
Α. A brief reading of "Vertical pumps", page 2-108 to 2-123 of "Pump Handbook" by Karassik, Krutzsch, Fraser, Messina (McGraw-Hill, 1976) has not indicated usual RPM range. However following notes could be useful a bit.
1. Concerning centrifugal pump inquiries in local work place: rotational speed is not specified, but a limit of 2900 RPM is usually stated for either horizontal or vertical pumps.
2. Pump specific speed (RPM*SQRT(GPM)/ft^0.75) is applicable for either horizontal or vertical pumps.
Β. Personal opinions (subject to criticism):
1. Usual RPM range is 1450 - 3600 RPM for either horizontal or vertical centrifugal pumps (slurry pumps can adopt lower rotational speeds, down to 725 RPM).
2. Vertical process pumps have higher maintenance cost compared to horizontal of same flow and head, at least according to some experience in fertilizers (1975-81).
3. Probably the query asks whether failure probability of a vertical pump gets higher than of a horizontal pump (same flow, head and RPM), as rotational speed gets higher and higher.
-For long vertical pumps (long shaft), impellers-shaft system balancing may get unstable (*) at high RPM, despite the intermediate shaft bearings. So mentioned long pump can be more "vulnerable" to high RPM , but there is no corresponding horizontal pump (no need of long horizontal shaft in practice).
- For a vertical pump of same number of impellers and length to an horizontal pump, RPM affect is probably same concerning probability of failure. Vertical or horizontal shaft of same length may have no difference in developed vibrations as RPM increases.
- A mechanical engineer specialized in pumps could clarify the above assumptions of para 3.

(*). This means more measures for a balanced system at high RPM, hence more cost of the pump (possible but expensive).

[Rahimzadeh]

Dear KKALA:
Thanks for comments.
I must say many things is unclear for me about vertical pumps.
1-what is main application vertically double casing multi stage pump(vs6)?
2-what percent of best efficiency flow rate must be designed as min flow for above mentioned pumps?
Best regards.
M.R.Rahimzadeh

[kkala]

1. Having recognized "vs6" pumps in http://www.flowserve...hueren/WUC.pdf , I have seen (or known) them used in liquid propylene, NH3, LPG, whenever low NPSH is required. Other advantage is their limited space.
2. Specific min flow requirements are not known (to me), however usual procedure here is to initially assume 30% of rated flow for any type of centrifugal pump (horizontal or vertical). Pump supplier specifies necessary min flow and corrections are made in detail engineering.

Edited by kkala, 14 July 2012 - 11:38 AM.

[ankur2061]

-what percent of best efficiency flow rate must be designed as min flow for above mentioned pumps?
Best regards.
M.R.Rahimzadeh

rahimzadeh,

Refer my blog on minimum safe flow at:

http://www.cheresour...ntrifugal-pump/

Regards,
Ankur.

[Rahimzadeh]

Dears:
As you know the minimum flow for multistage horizontal pump is few times of single stage horizontal pump but for vertical pumps this ratio become more higher.
For vertical pump the liquid temperature must be limited to 60 deg centigrade.
Another big problem for multistage vertical pump ,they could not handle light hydrocarbon because risk of firing.
I like you send me applicable information similar of above information.
best for all of you.
M.R.Rahimzadeh

[kkala]

1. Minimum flow of 30% has been assumed for several vertical pumps transferring hydrocarbons at ambient temperature (max 40 oC), according to post No 6. Actual min flows had not been known, project was canceled later.
Anhydrous NH3 vertical pumps (installed in fertilizers, 1978, ~30 m from consumption) had no minimum flow. I think they would have today.
http://www.eng-tips.....cfm?qid=266031 may be useful.
2. Not aware of liquid temperature limitation (60 oC); nevertheless pumped liquids mentioned in post No 6 were at ambient temperature (from pressurized storage).

Edited by kkala, 16 July 2012 - 09:08 AM.

[Rahimzadeh]

Dear KKALA:
Thank for your useful comments.
What is your idea about pumping the condensate with specific gravity of 0.75 in following condition:
LIQUID:
1-TDH :100
2-FLOW:3.5 M3/HR
PUMP:
1-RPM:2950
2-NO. STAGE:4
3-TEMP:13O DEG. CENTIGRADE
4-VERTICAL

THANKS
M.R.Rahimzadeh

[kkala]

In Process data sheets here, we specify flow rate, head, NPSHa for each centrifugal pump (whether it shall be horizontal or vertical is sometimes determined by us) and rest is left to Rotating Machinery Dept. The latter issues a more complete pump specification for bidders, where No of stages and RPM are left to bidders (but usual upper limit is 2900 RPM).
So I cannot assess data of pump in reference. What Rotating Machinery Dept does in such cases is to search the pump data bases of big pump suppliers. See http://www.cheresources.com/invision/topic/13367-vertical-can-type-pump/, post No 7 for an example in Flowserve database. The procedure needs some patience, but returns specific pumps according to requirements and with their characteristics. Flowserve needed registration 2 years ago, when a search was made by Rotating Machinery Dept in my presence.
Concerning mentioned temperature limit of 60 oC for vertical pumps, vendor or someone with experience could advise / confirm.

Edited by kkala, 16 July 2012 - 11:21 AM.

[Rahimzadeh]

Dear KKALA:
Thanks for your high value comments.
But our problem remains.
These pumps failure rate is too high in compare with horizontal ones.
I suggest that the application of vertical limited or at least the some parameter such as pump speed , liquid temperature, sealing liquid must be considered .
Best Regards
M.R.Rahimzadeh

[kkala]

I personally agree with you, http://www.cheresources.com/invision/topic/13367-vertical-can-type-pump/, but there are cases where vertical pumps cannot be avoided, mainly due to low NPSHa. Unfortunately, at least here, it is the mechanical (not chemical) engineer that knows mechanical details of pumps and potential problems (including maintenance).
In the fertilizer factory we used to record any maintenance of equipment (and the work about it), especially for critical pieces. If a piece of equipment had too frequent problems, we tried to diagnose the cause or tried another from other vendor.
Pair of vertical pumps (byron jackson ?) to transfer anhydrous NH3 from pressurized storage to NPK fertilizers (post No 9) had a rather satisfactory operation. But two first impellers were often found eroded. Probably it was due to insufficient NPSH, since the margin over NPSHr was taken as 2 ft. I knew later that liquids at their boiling temperature would require a higher margin.
Note 19/7/12: However I am not sure that this was the reason of eroded impellers.

Edited by kkala, 19 July 2012 - 01:04 AM.

[Rahimzadeh]

Dears all:
I got necessary meaning

Thanks