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FOR VT-300 CO2


 Vapor distribution systems are easily designed for almost any installation. Two factors must be considered. 1) The system must be designed to safely handle the 300 psi pressure of the CO2 to be distributed. 2) There must be minimal drop in pressure due to vapor flow at the satellite to be served.



No Insulation: A CO2 vapor distribution system does not have to be insulated because the CO2 vapor rapidly attains ambient temperature after leaving the bulk CO2 storage tank receiver. Uninsulated vapor distribution lines remain clear of condensation and icing whenever CO2 vapor is being transferred to the satellite reservoir.



Line Material: Dry CO2 vapor is inert so the choice of pipe or tubing is dependent only on pressure ratings. Copper tubing is readily available, inexpensive, light and very workable. For these reasons it is the primary choice in most VT-300 CO2 vapor distribution systems.



Pressure Ratings: Copper tubing for refrigeration and air conditioning use has pressure ratings sufficiently high for bulk CO2 vapor use. The table below gives the rated internal working pressure for several sizes of refrigeration tubing.



Rated Internal Working Pressure for Type ACR

Annealed Copper Tubing

Nominal Size

















900 psi


880 psi


740 psi






740 psi


730 psi


610 psi






740 psi


720 psi


610 psi






650 psi


630 psi


530 psi





590 psi


570 psi


480 psi






510 psi


490 psi


420 psi






460 psi


440 psi


370 psi






430 psi


410 psi


350 psi



Pressure Ratings and Burst Pressures: The pressure ratings above have been determined using an allowable stress that is a small fraction of copper's ultimate tensile strength. The actual burst pressure is many times higher than this, for example the measured burst pressure the 1/2" tube is 5900 psi.



Joining Tubing sections: The vapor system may be assembled using compression fittings, or permanently with solder-type fittings. If solder type fittings are used, use a brazing alloy or 95-5 Tin-Antimony solder do not use soft solder . A tin-lead 50-50 solder provides a joint with a pressure rating of only 200 psi.



Line Pressure Drop: Whenever CO2 vapor flows through a pipeline a pressure drop occurs due to friction loss. The magnitude of the drop is dependent upon the velocity of the flow, and the size and physical properties of the pipe. The velocity of the CO2 vapor is proportional to the rate of recondensing in the VT-300 units in pounds of CO2/hour.




Allowance for Bends and Elbows and Tees: Flow disturbances that occur at tube fittings add to the pressure drop substantially. For instance, an elbow on a 1/2" line is equivalent to about one foot added to the length. For a one inch diameter, add two feet to the length. The proper factors must be considered when laying the system out.



Peak Flow Rate for Small Systems: In small systems with only a few VT-300 CO2 Satellite reservoirs, the possibility that all satellites are recondensing at the same time is high. The peak flow rate should be used for design and calculated by adding the condensing rates of all of the satellite reservoirs. For example, a system with four VT-300-7 CO2 Satellite reservoirs would have four times the 20 pounds/hr flow rate for a single unit or 80 pounds/hr.



Peak Flow Rate For Large Systems: In large systems the probability of all stations condensing CO2 simultaneously is low enough to safely assume that only a fraction of the units will be recondensing at any time. If the maximum flowrate is assumed, the system will probably not need to be modified if more VT-300 CO2 Satellite Reservoirs are added.



Acceptable Pressure Drop: A pressure drop of 10 or 15 psi is acceptable for satisfactory operation of the VT-300 satellites reservoirs and the environmental chamber solenoid valves. The pressure at any satellite is the source pressure less the pressure drops in all segments supplying it. Select segment pressure drops sufficiently low, so that when added together the sum is less than 15 psi at all satellites.



Calculating Pressure Drops: In a single piping system with satellites spaced along it, add the average recondensing rates of all satellites to determine the flowrate in the first segment of the piping. The next section of pipe will have the mass flowrate of the first section less the recovery rate of the first satellite. The last section of the piping system would only have the flow-rate of a single VT-300. The average condensing rates for VT-300 CO2 Satellites are listed on the VT-300 price list.



Designing Trunk Lines: To determine the required pipe sizes for the system with branches start at the CO2 receiver and select a tubing size to accommodate the total mass flow for the system. Add up the average recovery rates for all of the VT-300 Satellite reservoirs. Using the pressure drop table select a tubing size that gives a pressure drop of 5 psi or less.



Designing Branch Lines: Calculate the pressure drops of branch lines by adding the average recovery rates of all VT-300 units on the branch. Smaller diameter tubing may be used since there are fewer VT-300 CO2 Satellite Reservoirs on a branch than a trunk. Generally two tubing sizes will satisfy the needs of an entire system. Each successive segment will have a lower pressure drop per 100 feet because the mass flow rate is reduced as each reservoir is passed. The total pressure drop at the end of any branch line should not be more than 15 psi under full flow condition.



Typical Calculation: Four VT-300-7 CO2 Satellite reservoirs, each with an average condensing rate of 20 pounds of CO2 per hour are fed from a line 500 feet long. The units are spaced 100 feet apart with the first VT-300-7 200 feet from the CO2 receiver.


Diagram 1

The mass flowrate in the first segment is 80 pounds per hour because all four VT-300-7 CO2 Satellites draw CO2 vapor through the first line segment. Referring to the graph, it is apparent that 0.5" OD tubing with a 1.7 psi/100' pressure drop is the minimum pipe diameter. The next size smaller tubing shown (0.375") has an unacceptable pressure drop of almost 8 psi/100'. The total pressure drop in the 200' first segment is 3.4 psi.

The second segment will have a flow rate of 60 pounds per hour because the first VT-300-7 CO2 Satellite has been passed. From the graph it is apparent that the tubing still must be 0.5" OD which has a pressure drop of about 1 psi for the 100' segment.

The third segment will have a flow rate of 40 pounds per hour with the load of the two remaining VT-300-7 CO2 Satellites remaining. The next size smaller tubing now can be selected because 0.375" OD tubing only has a drop of 2.11 psi per hundred feet at 40 pounds per hour.

The last segment with only the flow rate of the last VT-300-7 CO2 Satellite would have a pressure drop of less than 1 psi. for 0.375" OD tubing. The total pressure drop between the receiver and the last reservoirs would be the sum of the drops for each segment, 3.4 + 1.0 + 2.11 + 1.0 =7.51 psi. The total pressure drop of 7.51 psi is well within the 15 psi specified limit.

From a practical view point, it is likely that a single size of tubing will be used. This is a wise choice because it allows for future expansion of the vapor distribution system.

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