Adding stages to a VTP
Adding stages to a VTP
(OP)
Can anyone tell me why after increase the stage of a 10inch vertical turbine pump from 3 to 4 stages the flow fell from 288 m3/hr to 240m3/hr (1500RPM)instead of increasing. Please note the pump is operating in the same system. The system of operation is pumping directly inline.





RE: Adding stages to a VTP
RE: Adding stages to a VTP
Something left in the pump during the addition of the stage that is obstructing flow?
Some change in the downstream piping such as a valve partially closed?
Suction restriction?
RE: Adding stages to a VTP
RE: Adding stages to a VTP
1) check pump rotation is correct or not.
2) Check you installed the correct impeller.
Was the original pump with dummy stage casing before?
if not, the addition of another stage could push the suction closer to the bottom of the tank and cause inlet restriction and resulting in cavitation.
RE: Adding stages to a VTP
The discharge flow may only increase if the system curve that you are pumping against will allow more flow. If you have a pumping against a system curve consisting of mostly static head, then you should not expect more flow, just higher discharge head.
Vertical turbine pump stages (bowls) can be added in series. By doing this, the head capability is increased. The head-capacity curves and horsepower capacity curves are additives
at a given discharge. Head and horsepower are doubled if a second bowl is added to a first bowl; three stages would triple the head produced and horsepower required.
Adding stages usually means furnishing the pump initially with sufficiently large shafting and motor base to accommodate the increased future horsepower.
Does the existing motor have adequate HP for the new condition of 288 m3/hr @ 33% more HP or did you change the motor?
RE: Adding stages to a VTP
If the motor is undersized for the new stage, wouldn't the motor likely be tripping due to overcurrent? I can't see the slip increasing enough to reduce the flow if this is a standard AC motor.
Jamaican, what is the fluid you are pumping? You said you are pumping from an open tank so the vapor pressure of the fluid is the main factor in the available NPSH. You said that the discharge pressure had also dropped along with the flow, can you describe the system that this pump is installed in?
RE: Adding stages to a VTP
If lift is not the problem, I would be concerned with wear ring clearance, impeller pattern (cast for correct rotation), and impeller mounting. If the impellers are mounted to the shaft with tapered collets, an impeller could have come loose and not be spinning.
Some pumps of this type have internal porting within the head so that the seal chamber can be maintained at discharge pressure or suction pressure depending on the installation and removal of certain internal plugs. If plugs were not correctly installed, this could also provide a path for internal recirculation.
As Pumpsonly noted, you need to verify that the clearance between the pump and the sump floor did not change, creating a suction restriction.
Johnny Pellin
RE: Adding stages to a VTP
I saw this occur once when the Contractor incorrectly installed a pump too close to the floor, (as Pumpsonly suggested). The increased suction headloss caused the pump to operate off the pump performance curve.
RE: Adding stages to a VTP
Something else to think about, are the new impellers fitted backwards??
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Adding stages to a VTP
RE: Adding stages to a VTP
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Adding stages to a VTP
what type of tank and what are the dimensions?
RE: Adding stages to a VTP
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Adding stages to a VTP
You did not post any head figures before and after or any performance curve. So we will just continue to speculate.
A centrifugal pump will produce typically 50 -60% of the performance when in reversed rotation depending on the Ns. Assuming each stage produces 50 Meter at 288 m3/hr. A 3 stage pump in correct rotation will give 150M and 4 stage at 200 M. 60% of 200M = 120M. Bear in mind that now you only get 240M3/hr, the corresponding head on the curve would be higher. Therefore it would be 60% of >200 m. which would be just below the 150M head of 3 stage pump in correct rotation as you mentioned in your second post.
Any way please let us know what was the final finding.
RE: Adding stages to a VTP
RE: Adding stages to a VTP
High power (matches expected 4 stage requirements) - forgot to install wear rings, new impeller different hydraulic design (wrong part), leak in system somewhere before location you are measuring
Low power - suction issue (cavitation, vortexing, restriction), loose impeller
Note - it is uncommon to have a "dummy bowl" that is fully functional just minus an impeller. There will be losses in the dummy configuration, without an impeller to guide the flow through the bowl diffusers. It is more common to include a short column/spool piece that matches a bowl length, bearing location, and bolt circles/mounting details. This spool is then pulled and replaced with an actual bowl at the same time an additional impeller is installed.
Are these collet mount or ring/key? In theory you could throw an impeller wherever you wanted on the shaft if it is collet mount. If it was installed above a "top case" and discharging into an open column pipe, I can imagine that flow disturbance to have the symptoms you are describing. I have trouble thinking that this could actually happen, but you never know.
RE: Adding stages to a VTP
The NPSH requirement above 300m3/h is 53ft. What is the NPSHR at 288 m3/hr and 300M3/hr?
You were doing alright at 288m3/Hr which is not far from 300m3/hr. The NPSHr can not shoot up so much with small increase in flow. Unless you are operating very near to the end of the curve.