Flow field through a gate valve installed in a circular pipe and loss coefficient

Abstract

The loss coefficient and the flow fields downstream of the typical models of gate valves are investigated experimentally from the surface pressure and velocity distributions measured in the air-pipe flow at Reynolds number 4×10⁴ and the various visualization methods. The attention as the gate valve model is paid to the gate plate, which is an essential part of the various practical gate valves. The gate plate has three different fundamental shape types named convex-type, flat-type and concave-type, based on the shape of the plate head projecting from the inner pipe wall. The aim of this study is to clarify the effects of shape, height ratio and thickness ratio of the gate valve plate on the loss coefficient and flow field in the turbulent pipe flow. The height ratio is the relative height defined as the gate-plate height, which is the height from the inner-wall surface to the head along the center line of the valve plate, to the pipe diameter. It varies from 0.1 to 0.8. The thickness ratio defined as the gate-plate thickness to the pipe diameter is kept at 0.1 for the flat-type and concave-type gate plates, and varies in 0.1, 0.3 and 0.5 for the convex-type gate plate. As a result, the loss coefficient is strongly dependent on the shape type and the height ratio, and is slightly dependent on the thickness ratio. The shape type and the height ratio are able to be replaced by the open-area ratio to estimate the loss coefficient as one parameter independent on them. The necklace vortex is produced in front of the gate valve plate, and they flows downstream above the head of the gate plate. A three-dimensional recirculating flow region is produced behind the gate plate, and there is a strong secondary flow and a recirculating region longer than the center reattachment length along the symmetrical plane of the valve plate in the case of the gate valve plate with a small open-area ratio.