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That is very interesting. .we have been dosing the system almost daily with sodium hypochlorite, keeping it up above 1ppm. Although the hypo is tested before dosing to ensure its quality, that doesn't factor in possible suspended metal particulate already inside the system...I will pass that...

No worries, will do. ;)

Don't know what I was thinking there..I did the calculation, flow velocity is about 0.5m/s when going through the minimum flow line with discharge PCV closed. I have conferred with some colleagues, and the general consensus is that there is enough head from the water level in the tank to flood...

Sorry, there is a decimal point in there...the downward leg is about 1.0m. It then goes up about 6.0m to the top of the tank (for the kickback line) and 15.0m or so for the main distribution up to the pipe rack). Would the fluid velocity be less than 1m/s? I feel like it would be more than...

I see what you are saying...although wouldn't it be able to be noticed if air was getting through the NRV? Would I be seeing water pass through the NRV's as well? I just switched pumps back from A to B, and didnt have an issue (but B was only off for a couple of hours). One thing I noticed was...

Ok,I have attached a quick sketch I did (please excuse its crudeness, I could not find any isometric paper and have been a bit rushed tonight). A bit of info about it: - the pumps are at the same level - the inlet line is at the same level from the tank to the pumps - the pump discharge and...

Thanks for all the input gents..I think the reducer theory is the best thing to go on so far, but our RE is on leave, so will have to wait to see what he thinks. LittleInch, i took the head pressure from the tank height. The tank is always full, and is 5m high and open to atmosphere. The inlet...

I was thinking because the length of horizontal line between the tank and the pump is short, that may not apply...but I have looked at other water pumps in the same module, and I have to concur, since they also have the reducer positioned flat side on top. These pumps seem to be the only ones...

My apologies..this really isn't my night. I drew that up in a bit of a rush..the minimum flow line from the pump on the right ties in to the common line downstream of the check valve, not upstream as indicated. Sorry. - Joss

I agree...there has to be something else, and I have been scratching my head trying to figure out what that might be. Unfortunetly, staring at it isn't giving me the answer. Pump B has been running for about 4 days now, so I might try starting up pump A tomorrow and see if it has any issues as...

I had a look in the database...unfortunately no 3D CAD or iso schematics for this particular system (literally the only system on the plant without them). I could freehand draw it if you like, but might not do it much justice. haha.

The layouts are identical for both pumps, and both share a common 'Y' suction and discharge line. I will try and find an isometric drawing, but both pumps are at the exact same level. I have attached a cross sectional drawing of suction, pump and discharge (identical for both pumps) to give...

I had a look...the eccentric reducer does have the flat side on the bottom..and the supply line to pump suction is flat - coming straight off the bottom of the water tank at the same elevation. However, I would think that entrained air would be a once off occurence, no?..and this situation has...

Just as an afterthought, a bit of additional info about the system...For the past couple of years the water circuit has been springing leaks all over the place, so there is a bit of internal corrosion (i think due to the old RO water)...so i imagine there might be a bit of redox in the system...

Thanks for the replies. I have uploaded a quick sketch of the pump flow scheme (sorry, I should have done that initially). The idea of disolved air is intriguing...we have recently switched from desalinated reverse osmosis water, to normal town supply water, which has more minerals and much...

Hi all, I have a bit of an issue with a potable water pump on my site. We have two pumps in parallel, one duty, one standby (A and B). When changing over from A to B the last 3 times, the discharge pressure has dropped to zero. I have opened the casing vent on B pump, and there has been a lot...

Ah yes..that makes a bit more sense to me now (I know next to nothing about steam turbine units). haha

In case anyone is interested..I found a paper on the subject (relating to aircraft engines, but same principle). It seems like water ingestion will just cause steaming in the latter compressor stages and combustion chamber, eventually resulting in flame-out. Doesn't say anything about component...

I figured that was probably the case. I'll try and find some data on it..although if anyone has some anecdotal evidence I would be interested in hearing it.

Thank you also rotw.. I've never looked for any manufacturers specified tolerances for liquid carry over..I've just always been told 'no liquid in the compressor', which I think is a good rule to live by in general. I'll check out the data sheets for some centrifugals and find out. I don't...