| 摘要 |
A precompression metering pump has already been mounted on a pressurized receptacle in the prior art. It serves not only to propel the contents of the receptacle for spraying purposes, but also to isolate said contents from ambient air in order to prevent it being degraded. However, in the past such a pump has been provided with a return spring capable of raising the pistons of the pump to a rest position regardless of the pressure inside the receptacle. Consequently, should a leak arise from the receptacle, there has been a danger of delivering a substance that has been degraded by contact with the atmosphere. The present invention avoids this problem by making spraying impossible should the pressure inside the receptacle fall below a predetermined pressure which is advantageously chosen to lie in the range 1 bar to 2 bars above atmospheric pressure. This is achieved by reducing the stiffness of the spring so that the pistons are raised in part only by the spring expanding and in part also by the force transmitted by the pressure that exists inside the receptacle.
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