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higher than the 11 L/hr desired. (As the flowmeter was inoperable, seeding rates were estimated based on the number of ho~rs of seeding a~d that a fdl tank of proptine \l':as &;seJ). The SUP?!y line used from the propane tan.1( to the di:-.penser was a 9.5-nun flexible black high pressure hose. It was observed that the hose would absorb heat even at temperatures below freezing causing the propa~e to vaporize in the iiile thus causing line and internal plur.1bing freeze-u? This would render the dispenser inope.av~e. After mid-l\larch it was not possible to release liquid propaae due to this problem. On Marci. 20, the initial dispenser was removed from the field because of a radio transrr.itter component failure a:id a second dispenser installed. Since seedi:1g could not be initiated from this dispeaser due to supply line freeze-up, orJy communications reliability could be monitored d:.lri~g differe~t weatter conditions. It was deten:lined that racio commuIications even in the worst weatl1cr were excellent. After the second tower was instalkd, conun~nications was never a problem. This was verified by the fact that the station was automaticaHy polled each hour by the computer in Sacramento. The computer kept daily statistics Oil data received (see bottom line in Fig. 7). Although this first field program was limited in duration it idemified several major design problems with the remote dispenser. These were addressed as described in the foHowing section. 2.2 1989-90 DisDenser Design and Testing DOlring tl:e S;ltillIler of 1989, several m.ajor design changes were made :0 the dispenser. 1\ot only were there fundamen~al problems with the original design as described above, but there were also problems with performi3g field maintenance with the initi:ll design. This was especially true of the valve aGd plumbing assembly. With the nozzles and valve box separated, it was a major undertaking to replace solenoids or rep~ir leaks in plumbing. Thus the first design change made was to move the valve assembly to the top of the dispenser aGd ta..;e the nozzles protrude from the valve box. This allowed 6e box to act as the shield for the nozzles. In aGdition, ttis allowed removal of the valve assembly without having to remove the supply line from inside the square tubing. Copper tubing was then insura~ed using foam and reflective tape and cor..nected directly from the tank to the valve box at the top of tbe tower completely eliiTinating line freeze-up. Fig. 4 shows the modified valve assembly with supply line attached (uninsulated in this photo). As a further aid to field maintenance and seeding operations, the original five valves (two for the tanks and one for each nozzle) were replaced with three large filtered lock-off valves (filtering debris in the liquid propaile) to control the three nozzles, Fig. 5. This meant that the two propane tanks would be drawn down together. This not only simplified the plumbing but Figure 4 Modified propane dispenser used for the 1990 winter field program. Valve box is now at the top of the tower and acts to shield nozzles from icing. .r' ----~f_~ - ~ .;a ~:--- P.:.~ '!"......-- <:: Figure 5 Valve assembly showing flowmeter in-line with plumbing in foreground and three lock-off valves in the background. reduced the power drain during operation (each solenoid requires 1 A to operate). The nozzles were changed to a fiGe spray atomizing type for which Gow rates could be repeatedly obtained of 9.5 to 11.5 L/hr. These nozzles had an irJet diameter of 0.4 mm, requiring internal filters to screen any small particles not fLitered by the lock-off valves. The antenna design (folded dipole) was changed to ensure antenna integrity during extreme icing events.