Sticky Imperial hp pressure gauge

[desA]

Bought a news set of Imperial gauges - Deluxe 2-Valve brass manifold - Type 436-CKP.

I left them set on an experimental research heat-pump, which was running tests over a period of a few days. When the system settled, after power-off, the hp gauge seemed to fancy settling at around the 120psi odd mark - the lp gauge would rise up to something slightly less & there they sat.

Took the gauges off the machine yesterday & noticed the hp gauge doesn't drop back below ~ 110psi.

Re-connected the gauges to the machine, ran a trial & the hp pressure readings seemed to indicate normal pressures i.e. no pressure offset indicating a faulty reading.

Not quite sure why this hp gauge doesn't return to zero - am I missing something obvious? Operating fluid R-134A.

Be a shame to have to go off & get another hp gauge - this one only being a few weeks old. Confused. :confused:

[nike123]

Is it possible that somehow it is exposed to excessive pressures?

[desA]

^ A very good question.

Well, we did connect into a nitrogen system (I know, but wait) - through an argon regulator & flow-meter - the pressure never went above the 175psi mark. We are not able to get N2 regulators down here, but were very careful to not over-pressurise. The flow input was very slow & we let the system stabilise itself.

At no point was the system ever exposed to the direct N2 bottle pressure.

[desA]

The high-pressure line on this test heat-pump pushes a lot of oil out when the hp hose is disconnected - not sure if this is a normal thing. Wondered if the gauge was gummed up inside with excessive oil.

On this particular test-rig, the hp test point sits on line leading from a point near the compressor discharge (~ 6 inches), down into a high-pressure cut-out switch. Every time the hp hose is taken off this line, it does tend to spew a bit of oil & gas - thought that came with the territory on the hp side - although I'm beginning to wonder about the oil migration into the test line - seems excessive.

Do I need to go out & buy another gauge? The odd thing is that the upper readings seem to correlate with what the guage did when first used - it's not as though there is a permanent offset due to damage.

[nike123]

Try to clean it from oil with repeated pressurizing and depressurizing with alcohol filled hose pointed downwards and nitrogen and emptying/replacing alcohol in hose between subsequent pressurization's. If that doesn't help, it is probably damaged somehow and need replacement.

[nike123]

On this particular test-rig, the hp test point sits on line leading from a point near the compressor discharge (~ 6 inches), down into a high-pressure cut-out switch. Every time the hp hose is taken off this line, it does tend to spew a bit of oil & gas - thought that came with the territory on the hp side - although I'm beginning to wonder about the oil migration into the test line - seems excessive.




That depend on point where test line is connected at discharge line. I would connected it at vertical portion of line, not horizontal and at bottom of line (6 o'clock), and first it should go upward for some length and then where you want it to end.

[desA]

^ ^^ Thanks so much for your excellent advice.

I'll work on the alcohol cleaning/ N2 flushing - excellent idea.

The current hp test line leading from the discharge line comes off the line at the top of the pipe, vertically upward for around 3 inches, then loops in a sweeping 180' bend, heading downwards to the Ranco set. The test point is located on the long vertical line on the way down to the Ranco.

I inherited this heat-pump unit, & am re-working it into a better system - this is one area where some serious re-work will be required, it seems. Surely the Ranco's should be higher, than lower?

The discharge line is also set to undergo some routing modifications in order to set in oil traps, & a decent riser. This should allow me to set up a decent test point in line with your recommendations. (Anyway, I digress)

[Brian_UK]

Does the new manifold set have a non-return valve in the high pressure connector?

The type to stop blow-back when disconnecting..

[desA]

^ Hi Brian,

Only re-visited this thread today & missed your addition.


Does the new manifold set have a non-return valve in the high pressure connector?

What would this non-return valve look like? I've been connecting into a service port, & its Schraeder valve, using the Imperial hp hose into the gauge manifold.

[Brian_UK]

Do you get any blow-back from the hose when disconnecting?

If not then there could be a NRV in there somewhere.

[desA]

Certainly do get blow-back at high-pressure, plus a spray of oil. Seems then that it has no NRV.

What hoses typically have an NRV?

The blow-back issue & oil-spray is a nuisance.

[desA]

Feedback:

HP gauge is now clear.

It was definitely clogged up with oil. Yesterday, I modified the service ports to slope gently upwards, off horizontal orientation (self-draining) re-connected the gauge set with the hoses in an almost vertical orientation & ran two high temperature trials on the prototype heat-pump.

Left the gauge set on all night, disconnected this morning & viola - the HP gauge was all sorted.

What had happened was that this particular heat-pump prototype has service ports that lead off lp/hp lines running downwards to the Ranco lp/hp cut-out switches. The service ports lay off horizontally from the vertical lines. I had connected the gauge manifold at slightly below the service port level, probably allowing oil to flow into the gauge - a silly move in hindsight.

Nike123, I owe you a coffee.

[nike123]

Nike123, I owe you a coffee.

Thanks, I am glad that you sorted it.