(under subclass 323) Glasses of the type commonly employed in boiler installations and comprising a tubular conduit, transparent at least in part, connected at one end to the space above the liquid in the reservoir and at the other end to the reservoir below the normal liquid level so that the pressures on the liquid in the reservoir and gauge may be equalized.
SEE OR SEARCH THIS CLASS, SUBCLASS:
293, and 326, for boiler type glasses equipped with guards or casings.
297, for boiler glasses combined with water columns.
299+, for sight glass structure, in hydrostatic pressure gauges.
747+, for U-tube pressure gauges.
SEE OR SEARCH CLASS 285, Pipe Joints or Couplings, principally
