NRV on Pump Discharge line not lifting (100%)...

[Fabian Antao]

We have three pumps. The size of the NRV is 600mm. The pumps are operated with Soft Starter.
When first commissioned the pumps, the pumps operated fine.

The NRV's lifted completely and there would be a pressure reading of 0.8 bar.
Now into, 3 months of opeartion, the NRV's are not lifting when the pump is ON.
The pressure shown on the pressure guage is 2.0 bar. Pressure gauage is positioned after the discharge valve. (Pump --> NRV ---> Disharge Valve--> Airvalve)
We literally have to support the arm of the NRV, to OPEN it to full position.

All the three NRV's are behaving in a similar fashion.
This is causing low discharge flow from the pumps.

It's a three pumps system, 1 Duty, 1 Assist & 1 Stand by

Soft Starter is ABB (PSTX370-600-70)

Limit
Current limit type - Normal
Current limit level - 3.0 xle
2nd curr lim level - 7.0 xle
2nd curr lim time - 8 sec
Torque limit level - 150 %

Start & Stop
Start Mode - Voltage Ramp
Stop Mode - Voltage Ramp
Start ramp initial level - 30%
Start ramp - 5 sec
Stop ramp and level - 30 %

Would appreciate if someone could help me understand how to overcome this situation.

Thanks in advance.

 

[Rputvin]

Have you contacted the manufacturer of the NRV to ensure you're not operating the valve in a manner than would cause something to wear out in 3 months?

What fluid are you pumping and what materials are the seats of the NRV? Material incompatibility could be causing swelling in the seals which would cause the NRV to drag.

All 3 valves are behaving identically - how much run balancing have the pumps had? Has pump 3 only been run a few hours over the last 3 months, or are you changing lead pump frequently? If you are changing the lead pump, what is the procedure for the changeover?

 

[1503-44]

Perhaps your pump's low discharge flow is not sufficient to open the valves. You could post your system details. You have said nothing about the pumps, capacity, power, flow rate, pump curve and nothing about your system.

 

[Artisi]

Please clarify, was the initial 0.8 bar the system operating pressure which now reads 2.0 bar, if this is the case it seems more like a system problem, but as 1503-44 has said, we aren't clairvoyant.

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.)

 

[LittleInch]

know this is going to sound stupid, but they are the right way around?

What is that strange contraption on the shaft -?

Can you post a diagram of the NRV as the shaft seems to be in the centre of the valve?

But yes, need velocity / flow

Is that pressure or differential pressure across the NRV?

First guess is that you need to lubricate that moving shaft or look at anything else which has changed since you first started.

But if this is simple swing check then that last 20-30% of lift is quite difficult for the flapper to achieve and the weight plus a small amount of extra friction from that external shaft will make all the difference.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Electrical cable going to NRV - looks like an electrically powered NRV, or is it just a electrical position switch on the NRV. Can you explain?

 

[TugboatEng]

I believe that is not an electric cable but a hydraulic hose. The cube is a small reservoir. I believe I see a hydraulic cylinder that could be acting as a damper to prevent the valve from slamming.

 

[bimr]

Yes Tugboat, that is a check valve equipped with a hydraulic damper.

 

[TugboatEng]

I think that is important. What kind of valving controls the damping?

 

[Fabian Antao]

Electrical cable going to NRV - looks like an electrically powered NRV, or is it just a electrical position switch on the NRV. Can you explain?

It is an electrical position switch on the NRv. It's not electrically powered.
It's a check valve. The hydralic oil, is to avoid the hammer, when the pump stops.

I will share the drawing of NRV as soon as I get hold of it...

Thanks guys for the comments...