simple orifices of various sizes replaced the manual ballast valve.
Figure 9. Manual ballast valve.
(2) Displacement Switch
The displacement principle in ballast control has been used in two different types of valves. The first of these, called the "automatic ballast valve," used a needle valve, controlling ballast flow by an aneroid capsule to which the needle was attached (Figure 10). The aneroid capsule was open to the atmosphere on ascent; as the balloon began to descend to a region of higher pressure, a minimum pressure switch was used to seal off the capsule and further descent caused ballast flow. (For details see Technical Report No.1, Constant Level Balloon Project, Research Division, College of Engineering, New York University, New York, N.Y., 1948.)
There are three undesirable features of this system. Greatest is the effect of temperature changes on the air sealed in the capsule. Seal-off pressure acts as a datum plane. Any increase from this pressure causes compression of the aneroid, and ballast flows proportionally to the difference from seal-off pressure. However, with changes of temperature of the entrapped air, the activation pressure of the valve changes, the floating level is thus also a function of temperature of the gas in the aneroid.