Anti reverse rotation arrangement 1

[Samingme755]

Hi
our pump vendor propose that Anti reverse rotation arrangement cannot be provided due to limitations of manufacturing for fire water pumps electrical and diesel pumps and i am asking
if its normal
thanks really appreciate the help

 

[crshears]

Have pump discharge check valves stopped working and nobody told me?

 

[TenPenny]

Is this a vertical or horizontal pump?

NRR (non reverse ratchets) are pretty standard on vertical pumps with hollow shaft motors. They are extremely rare on horizontal pumps, I remember one customer wanting to investigate such a thing about 5 years ago, I wasted about four days trying to find something that would work, until we agreed that it was totally impractical.

 

[LittleInch]

Can't think of ever asking for this. Normally you find other methods of preventing reverse flow ( non return valves (sometimes two different types in series), actuated isolation valves etc.

Especially with FW pumps, there is very little you can do the standard approved model and design.

Who decided this was required and why?

 

[EdStainless]

We never used NRR, but we did use sensors to prevent trying to start a motor if it was turning backwards.
This was incase the check valve failed.

 

[Artisi]

Why would a fire pump run backwards?
You should ask why this question from whoever raised the requirement.

 

[JJPellin]

These mechanisms are common and necessary on some big, vertical well pumps and fire water pumps. Depending on the length of the pump, it will spin in reverse on shutdown even if the check valve holds. We had deep well pumps with 400 feet of line shaft. The vacuum developed at the check valve cannot support more than 32 feet of water.

 

[SB1976]

Anti reverse rotation (paul-and-ratchet mechanism) is generally a common requirement for Vertical pumps. This is because during emergency trip of the pump, there is an amount of fluid that would be accumulated in between the pump delivery flange and the non-return valve, which would flow back to the pump suction. This back flow would be responsible to turn the impeller in reverse direction. Higher the discharge volume, higher would be its ability to turn.

Now, if vendor cites inability to provide anti reverse rotation feature in his offered design, nothing can be done much as far as pump design is concerned. The only thing that needs to be ensured is that non return valve is placed very close to the pump delivery flange as reasonably practical as possible.