ANSI/HI 9.6.4-2009, Vertical Turbine Pumps & Vibration

[FuriousG]

I have a consultant engineer specifying the following vibration criteria for canned vertical turbine pumps:

Less than 1.06 mils, peak-to-peak displacement, in the direction
of maximum amplitude at a maximum peak velocity of 0.10 in/sec at
any speed within the operational range. The vibration measurement is to be taken at the top motor bearing.

This stringent requirement is well below ANSI/HI 9.6.4 for Type VS6 pumps (i.e. canned vertical turbines). Furthermore, the vibration measurement is taken at the top of the motor. ANSI/HI allows the measurement be taken at the lower motor bearing where the motor meets the discharge head.

Some useful info. on this VFD driven pump is as follows:

- 5,000 gpm
- 60 hp
- ~400 to 885 RPM

All of my pump vendors say this either can't be done with vertical turbine pumps or they will not guarantee the vibration level.

In the case where I need to comply with this vibration level, what extraordinary measures can be taken to meet this spec.?

 

[Tmoose]

I'd be interested in how many other vertical pump installations the consultant has worked on, and how the acceptance process went.

I'd say 1X and blade pass are likely to be what give you trouble aplenty.

Right away the numbers don't jive real well. If we are talking unbalance / 1X vibration at 400 cpm then 0.1 ips pk pk = over 4 MILS pk-pk
At 885 rpm 0.1 ips is still over 2 MILS p-p.
Blade pass for a 3 bladed impeller starts to approach some parity.

Some amount of bracing or stiffening should help.
Tuned absorbers and slight stiffness re-tuning can work slick, but only for single speed pumps.

But the VFD is going to go hunting ruthlessly for resonances, and it is rare for vertical pumps not to end up with a few resonances right in the operating range somewhere. Pump volutes are by nature flexible due to open curvatures, and are often the main part of the structure. A really stiff mounting would have to bypass the volute.

I've been on both sides of that process, and I don't envy you if you can't get some relief.

 

[Spud6414]

Can't be done.

Spud says; Meticulous effort and willingness to learn are honorable traits.