McQuay strange pumpdown / LLSV setup

[terminator]

Hi Guys,

I was looking at a McQuay air cooled screw chiller today and was wondering if any of you can elaborate on the pump down setup.

Rather than the usual llsv, it has a solenoid in the suction line. This solenoid takes liquid from the main liquid line before the tev, it goes through the solenoid once energized and goes to what would be the external eq connection on the tev.

I'm assuming that the liquid acts against the bellows in the tev and forces it to open?
When the valve is de-energised it seems to allow the tev to close and thus the system pumps down. However, this solenoid is connected into the suction line. Does the suction pressure act in accordance with this valve to also control the ext eq function of the tev?

I can't really figure out this strange set up.

Can anyone elaborate please?

[stufus]

It sounds like a pilot operated valve.Have a look through this thread from a while back it's all covered
http://www.refrigeration-engineer.com/forums/showthread.php?31838-Why-the-solinoid-valve&highlight=pilot+operated

Cheers
Stu

[install monkey]

ive looked at a manual and it shows hot gas bypass setup-whats the model number-ive got a few manuals

Hot Gas Bypass (Optional)
This option allows the system to operate at
lower loads without excessive on/off
compressor cycling. The hot gas bypass option
is required to be on both refrigerant circuits
because of the lead / lag feature of the
controller.
This option allows passage of discharge gas
into the evaporator inlet (between the TX valve
and the evaporator) which generates a false
load to supplement the actual chilled water or
air handler load.
Note:
The hot gas bypass valve will not
generate a 100% false load.
The pressure regulating valve is a Sporlan
HGBE-8 and factory set to begin opening at
102 psig with R-410a and can be changed by
changing the pressure setting. The adjustment
range is 75 to 150 psig. To raise the pressure
setting, remove the cap on the bulb and turn the
adjustment screw clockwise. To lower the
setting, turn the screw counterclockwise. Do
not force the adjustment beyond the range it is
designed for, as this will damage the
adjustment assembly. The regulating valve
opening point can be determined by slowly
reducing the system load while observing the
suction pressure. When the bypass valve starts
to open, the refrigerant line on the evaporator
side of the valve will begin to feel warm to the
touch.
The bypass valve includes a solenoid valve that
is controlled by the MicroTech II controller. It
is active when the first stage of cooling on a
circuit is active

[Brian_UK]

Which model is it?

Can't see that pipe make-up in their manuals but maybe looking at the wrong ones.

http://www.mcquay.com/McQuay/home/homepage
"Literature Search"

[edit]Go and feed the cat and get beaten to the reply.

[Mick13]

i have the same system at a site i frequent, the solenoid when energized will feed suction pressure to the external equalizer line on the txv, and when it wants to pump down it de-energizes and instead sends high-side pressure up the external equalizer line, hence forces the txv to shut and pump down.


edit: just re-read my post and noticed it doesnt explain what i mean so well, so here goes

we know that a txv has 3 forces in it, 1 opening force and 2 closing forces. the pressure from the bulb, (suction line temperature) is the opening force (as suction line temperature rises it opens the valve to let more refrigerant through). The 2 closing forces are from the superheat spring and the suction pressure from the external equalizer line. With that being said, if u put a higher pressure (from the high side/liquid line) onto the external equalizer line it will force the valve to close, and hence pump the system down.


the solenoid your talking about (if its what im thinking) is a 3way valve, one line from the suction, one line from the liquid line before the txv and one line going to the external equalizer port on the txv. in normal operation, the valve is energized and is allowing suction pressure up the external equalizer line and operating normally. When the system wants to cycle off/pump down, the valve de-energizes and instead of allowing suction pressure up the equalizer line it instead puts high side/liquid line pressure up it instead, then with the higher pressure on the txv it forces the valve to shut, and the system pumps down. Then once the valve energizes again, it returns the suction pressure back onto the equalizer line, this pressure is alot lower than the bulb pressure due to it having pumped down, the txv opens and lets refrigerant through, and everything starts up again.

[terminator]

Thanks Mick and others.
Apologies for my late reply.
I was being a thikko and sussed it out a couple of hours after my post...