Refilling process chiller loop

[Pykester1]

Hello
I have been working recently on a Carrier 30RA-40-240 240kw process chiller that supplies chilled water/glycol mixture to a factory installed AHU. I am experiencing problems associated with poor flow and pipework shaking which leads me to believe there is insufficient fluid in the loop, so I would like to top it up.
The pipe run is approx 25 metres horizontal (on the factory roof) and 6 metres vertical up the factory wall. The chiller is situated at ground level. The pipe flow and return is 3" PVC pressure pipe. I will estimate the freezing level of the fluid already in the loop first with a refractometer. There is one circulating pump in the chiller with one water pressure gauge and there is an auto vent on each flow and return pipe at the highest point (on the factory roof). I intend to use a high head pump and tank to refill the loop. Is there a method for knowing when the loop is completely full using the gauge, or is it a case of draining the system completely and calculating the volume of the loop etc and then refilling the exact quantity based on the required volume?
Thanks in advance for any responses.

[chemi-cool]

If the pipes are shaking, you got air in the system,
Check that your air vent works properly. and it is in the highest point of the pipes, 2 air vents you need one for each run.

[DTLarca]

Ideally you would have a pressure of 1 bar at the highest point.

That is to say that the lowest pressure in the system would ideally be 1 bar above atmosphere.

For a horizontal pipe run this would be at the suction of the pump.

Some pumps, depending on the water temperatures, will want as much as 1.5 bar net positive. But this is ordinarily relevant only to high water temperature conditions.

You simply keep topping up, as air is released, with a hand pump, mobile electric pump or pressurisation unit, till you have that 1 bar with smooth flow.

If the air has been in so long as to cause champaign water then you will be there a long time and the pumps might trip on overload every now and then and it might even turn out to be quicker to drain all for safe disposal and start again.

For 25% glycol by volume you probably have around 60 litres of it in there. Maybe £150 worth.

You would be looking to safely dispose of some 240 litres of water/glycol mix.

[redroge]

Run pump for ten minutes, switch pump off check theres a positive pressure in the system and allow air to rise to top of pipework if theres no air coming out of aav,s they could be faulty