Due to me volunteering (idiot!) I've been tasked with investigating why our SJAEs aren't functioning as they should. We run 2 100% duty ejectors, supplied by Nash Weineck, but for the last 8-10 years have had to run them in parallel under all load conditions to maintain vacuum in our condenser (16 year-old 360MW combined-cycle power station). In previous years the steam side has been stripped & inspected but the water side has been left alone. The inlet steam conditions are always consistent and the water flow through the ejectors is at 12 barG and around 40 degC.
I am going to contact SVS STRAHLPUMPEN und VAKUUM SYSTEME GmbH & Co.KG, Weineck's successor, but wondered if there was anyone else I could try that was UK-based?

Are you sure the problem is with the SJAE and not additional air in-leakage to the condenser?  Some SJAEs include a flow measuring device on the air discharge.  If so, you may want to compare the discharge flow at present with past readings.

Best of luck!

We do have a leak at present but not normally. As far as air flow measurement goes, they came fitted with vertically-mounted glass-bodied flowmeters with a metal bobbin inside to indicate flow, but these had a habit of jamming in their tubes and so the bobbins were removed many years ago. I did try and get the bobbins re-fitted a year or so ago but the same thing happened and I didn't pursue it.
We also don't have any way of measuring condensate flow to drain from the steam side of the condensers so we could well have a tube leak and not know about it.

Has anything materially changed with respect to the motive steam?  Is the motive steam (temperature and pressure) what the jets are speced for?  

Has anything materially changed with respect to the after condensers (plugged tubes, fouling, cooling water source or temperature or flow)?

Jets are pretty steady state devices and if they are operating within their design parameters they will usually either work or not.  If not, it is something wrong with the jet itself, such as nozzle wear or leakage of the motive steam around the nozzle threads.  You might want to consider a nozzle replacement.  If the answer to the first question above is yes in that the motive steam is not what the jet was originally designed for (different pressure, more or less superheat, etc) then you guaranteed want a nozzle change.

Try this.  Shut off the suction to the condenser momentarily and see if the jet (or jets) will pull down to a deep vacuum.  If not, it is the jets.  If you can't do this because the condenser back pressure climbs too high while the jets are isolated, then it is guaranteed your leakage rate is more than the jets can pull out.  If the jets pull down to a deep vacuum then again it is your inleakage overrunning your jets.

Give it a try.  What I have suggested is an old trick used by Jet service engineers to get a quick look for a place to start because if the jets are working, their reaction is very predictable-they will pull down quickly.

rmw

The other trick is to find a service company with some gas analysis equipment (RGA mass spectrometer).  They can tap the line leading to the SJAE and analyze it.  Is it all air???
Between rmw's suggestion and this you will have a better picture of what is happening.
My money is on severe air inleakage.

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Plymouth Tube

As noted by rmw, a few years ago we had major problems with the steam ejectors on a similar-sized unit which was eventually traced to a badly fouled condenser on the vac skid. Once the condenser was cleaned the performance improved noticeably.
  

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If we learn from our mistakes I'm getting a great education!