Spray technique local leak test

In order to avoid a surge of helium when the spray valve is opened (as this would contaminate the entire environment) it is advisable to install a choke valve to adjust the helium quantity, directly before or after the spray pistol (see Fig. 5.15). The correct quantity can be determined easiest by submerging the outlet opening in a container of v/ater and setting the valve on the basis of the rising bubbles. riable-area flowmeters are indeed available for the required small flow quantities but are actually too expensive. In addition, it is easy to use the water-filled container at any time to determine whether helium is still flowing. 

The helium content of the air can also be detected with helium leak detectors where large leaks allow so much air to enter the vessel that the 5 

Avoiding the helium surge when the pistol valve is opened 

Minimum helium quantity for correct display Changing the setting for the throttle shall not affect indication. 

The minimum quantity is always much smaller than one would set without a flowmeter (e,g, by listening for flow or letting the helium flow across moistened lips). The simplest check without a flowmeter Letting gas bubble through water. 

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