Plug Cock Valves
A plug cock (Fig. 7.63) is a manual valve that has a conical plug rotated in the tapered bore of a valve body. The conical plug has either a straight- through port (on/off) or ports arranged in a tee configuration (three-way ports). Three-way plug cock valves allow 90-degree changes in flow direction of both food product and cleaning solutions. Although they have good internal flow design, they are relatively expensive and have the disadvantage that
FIGURE 7.62 (A) A typical design of a double-seated mixproof valve consists of a valve hous
ing with an upper valve chamber (1) and lower valve chamber (2). Between the two chambers the valve seat area is arranged with two seats, usually one on top of the other with a separation cavity (3) (vent space) in between. The seats consist of an upper closure device (4) and a lower closure device (5), typically a disc, which are connected independently to the upper shaft (6) and lower shaft (7) for opening, closing and individual seat lifting. The cavity acts as a leakage chamber (3) and is open to the atmosphere via a drain pipe in the bottom shaft (8) for leak detection (outlet of the vent pipe must be visible for leakage!!). In the closed position, the upper valve chamber (1) and the lower valve chamber (2) are each sealed by the two valve disks, held independently on their seat by spring pressure. (B) To open the connection between the upper pipeline (9) and lower pipeline (10), the actuated lower valve disk (50) is raised off its seat first and then moves upwards a short distance before contacting the upper valve head (40). As a consequence, the drainage chamber (30) between the upper and lower body is gradually decreased. (C) Both valve disks then move further together into the open position. Meanwhile, in the more modern double-seated mixproof valves, the remaining cavity between the upper and lower valve disks remains sealed against the product area (11). It is important that the lower plug is hydraulically balanced (12, balancer) to prevent pressure shocks from opening the valve, hence allowing products to mix. When the valve closes, first the upper plug seals and then the lower plug seals. Both opening and closing of double-seated mixproof valves may show very small product losses getting into the cavity between the two valve discs during operation. However, this cavity can be flushed clean with cleaning fluid via a hose connection (13). The cleaning fluid will drain to the outside via the bores (14) and drain pipe (8) of the lower closure device. ln aseptic applications, steam or a sterile barrier may be applied in the atmospheric opening (vent) to prevent ingress of microorganisms. Courtesy ofGEA group AG.
FIGURE 7.63 Plug cock valves are unsuitable to be cleaned in-place, because product can get caught around the clearance between the plug and the valve body during rotation of the plug in the turned-off position. But, as they are easy to dismantle, they can be cleaned manually.
Courtesy of Sanitary Solutions, Inc.
FIGURE 7.64 With respect to plug cock valves, product can get caught as a thin stagnant film around the clearance between the plug and the valve body during rotation of the plug, and finally may leak to the outside. Courtesy of Mondelez International, © 2016.
they neither can be automated nor cleaned in-place. They are unsuitable for CIP, because product can get caught as a thin stagnant film around the clearance between the plug and the valve body during rotation of the plug in the turned-off position (Fig. 7.64). Bacteria can also gain access via this route. However, due to their simple design, plug valves are easily to dismantle for manual cleaning. They are also self-draining (CFCRA, 1997; Schonrock, 2005; Moerman and Kastelein, 2014).
FIGURE 7.65 Manual control valve with variable-flow plug. Courtesy of Tetra Pak Processing Systems AB; From Bylund, G., 2015. “Building-blocks of dairy processing ”, Ch. 6, section 6.8 — Piping, valves and fittings, Ch. 21. In: Teknotext, A.B. (Ed.), Dairy processing handbook. Tetra Pak Processing Systems A/B, Lund, Sweden.
