Sniffer valve

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A sniffer valve is a valve that opens when there is negative pressure and allows air to pass through until the negative pressure disappears. It has various uses in automotive, pumps, turbines, and plumbing.

Automotive engineering

In the automotive sector, a poppet valve was a form of valve control in four-stroke engines that was common until the beginning of the 20th century . The intake valve is not mechanically positively controlled , for example via a camshaft . The valve is only opened via the negative pressure that occurs in the combustion chamber during the intake stroke . At the end of the intake stroke it is closed again by a spring.

The disadvantage compared to mechanically operated valves is, on the one hand, a pressure loss, since the air flowing in has to keep the valve open against the force of the spring. On the other hand, the sniffer valve is not sufficiently speed-resistant for modern engines. In order for the valve to open sufficiently, the spring would have to be relatively weak, but then it can not close the valve quickly enough at a higher speed .

In diaphragm-controlled two-stroke engines , a flutter valve is used as a special form , in which an elastic membrane (often steel) forms the spring and valve body at the same time. In contrast to the four-stroke engine, the valve does not have to withstand the full compression pressure here.

The breather rubber of the oil filler neck on the crankcase is also referred to as the sniffer valve; this component was installed in various Citroën , Peugeot and Renault models, including the Citroën 2CV ("duck").

Piston pump

Aside from automotive technology, sniffer valves are also used on piston water pumps , but also on pistonless pumps (e.g. hydraulic rams ). With each stroke, a small amount of air is sucked in through the sniffer valve. It serves as the attitude of the air cushion in the connected pressure vessels ( air chamber , Hydrophore ). This enables a discontinuous pump to deliver a relatively continuous mass flow.

Sniffer valve of a piston pump Löwe Wasserknecht WL 1500

turbine

In cross- flow turbines for generating electricity from hydropower, they are used to keep the water level below the rotor constant so that it does not wade in the water and thereby slow it down.

Sanitary

Sniffer valves are also used in the sanitary area , for example when a washing machine and a normal sink use the same sewer pipe. The sniffer valve is installed after the siphon on the wash basin and prevents the lye pumped out by the washing machine from pulling the water out of the odor trap.

Trivia

The expression "Schnüffelstück" became known through a scene in the film Werner - Beinhart . According to the further course of the dialogue, however, an automatic vent valve is meant and not a valve in the sense of this article.

Individual evidence

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