The new two-component gas flow control for PMD consists of a single pass system for the constituent components (Argon and CO2).The schematic diagram is as shown
1) CV1, CV2: Circle seal check valves
2) M1, M2: Manual control valves
3) FM1, FM2, FM3: Volume Flow meters
(Vogtlin make -25l/h,16l/h & 40l/hrespectively)
4)NV1,NV2,NV3: Needle valves (part of flow meter body)
5) PG1, PG2: Pressure gauges (1Bar)
6) SV: Circle seal Safety release valve (1 Bar)
7) QC: Quick release couplings
Gas mixing tube and Glass bubblers
Individual gas components (Ar & CO2) enter the corresponding flow meters through the one way check valves (CV1 ,CV2) and manual control valves (M1, M2). Flow rates can be adjusted by the needle valves (NV1, NV2) located on the bottom part of the flow meter body.The metered gases enter a gas mixing tube and due to the concentric tube arrangement inside the mixer, the gas components change flow direction thrice thereby achieving the required mixing. In the event of excess pressure above 1 Bar, a safety valve at the exit of the mixing tube vents out gas, to protect the chambers.Flow meter FM3 indicates the total flow of mixed gases into the chambers. Return gas from the chambers is vented out into the assembly area after passing through the bubblers.
Quick release couplings are used at supply input connections and also for the chamber lines. Standard swagelok couplings and tubing are used for all connections.
The normal mass flow mixing ratio used is 70% Ar and 30% CO2
The normal flow rates used are about 30l/h total flow
1)Check connections to the corresponding supply lines (Ar & CO2) at the rear of the control panel.
2)Fully open Needle valve NV3.
3)Open M1 and M2 to read pressure on Dial Gauges PG1 & PG2 at around 0.8 Bar.
4)Adjust Argon flow by NV1 to 20 l/h on the flow meter scale.
5)Adjust CO2 flow by NV2 to 8 l/hon the flow meter scale.
6)Check total flow through FM3 (28 l/h on the flow meter scale).
7)Observe bubbling (takes a few minutes to appear).