The safe transfer of LPG in and out of large tanks on trailers or on truck chassis is critical to the LPG industry. The safe transfer of LPG in and out of large tanks or on truck chassis is critical to the LPG industry. Photo: iStock.com/skhoward A key step in such transfers is the opening and closing of the tank’s internal valve. This article offers a more operator friendly sub-system for the opening and closing of this internal valve that is more cost-effective in the long term, as well as safe. Too frequently the operator/driver of the trailer/tanker faces this dilemma: You just opened the liquid internal valve to unload your trailer or storage tank and started your pump, but the 427-2 liquid internal valve or the 404 liquid internal valve (depending on what is installed) slams shut. This sudden closure prevents any product flow, and this condition will last until the pressure on both sides of the valve equalizes. This lengthy pressure-equalization process can cause extensive (and expensive) delays and may also damage the pump. Further, the slamming of the internal valve shortens its life. Industry practice to prevent this internal valve from snapping shut is to install a sy...