| 摘要 |
A frost-free water supply system drains down to avoid freeze-up during non-pumping periods, its operation being responsive to air pressure within the system. A compound hose used may have an inner hose part co-extruded with the outer hose. The inner hose portion is preferably of flattened section, which facilitates threading of the inner hose within the outer hose, when not co-extruded. The compound hose with a flattened inner section, when its air cavity is sealed at atmospheric pressure conditions, provides an inbuilt air cushion that can generate initial de-watering pressure as high as about 716 gms per square cm (10 psi). The elastic memory, due to its initial flattened shape, also contributes to the de-watering capability of the inner hose. One unepected result, upon draining the liquids, is an unusual "bump" in the residual pressure of the air trapped within the outer hose, whereby the inner hose is more thoroughly flattened and more completely de-watered. Natural or synthetic rubbers may be used, parcticularly for the inner parts. The sealed enclosure of the pipeline by way of the end-fittings when under atmospheric conditions, ensures that in the drained condition the entrapped air returns substantially to atmospheric pressure. As this state prevails for much of the time, the likelihood of air leakage is greatly diminished, while the adverse effects thereof are minimized.
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