Venturi valve

Moving valves can have a sharp or a smooth ( venturi ) orifice. The venturi valves have one-half the dry pressure drop of the sharp-orifice valves, but are far more prone to weeping and channeling than the sharp-orifice valves. Sharp orifices are almost always preferred. 

Low dry tray pressure drop. On sieve and fixed valve trays, this means high (>11 percent) fractional hole area. On moving valve trays, this means venturi valves (smooth orifices) or long-legged valves (>15 percent slot area). On all trays, the channeling tendency and severity escalate rapidly as the dry pressure drop diminishes (e.g., as fractional hole area increases). 

VCFC is usually avoided by limiting fractional hole areas, avoiding venturi valves, and using forward-push devices. Resitarits and Pap-pademos [ Paper presented at the AIChE Annual Meeting, Reno, N ev. (November 2001)] cited tray inlet inactivity as a contributor to VCFC, and advocate inlet forward-push devices to counter it. 

The low-level filling system that has become the most popular in Northern Europe is the induction hopper. This commonly comprises a bowl of approximately 0.5 m dimension into which chemical is poured manually. Most bowls now use a Venturi valve arrangement positioned at the base of the hopper to suck material from the bowl into a liquid flow, that is then directed to the main sprayer tank. An alternative direct connection of the induction hopper to the input side of the main pump is much less popular, because of the potential to damage the pump from extraneous materials that could be introduced via the hopper. A typical induction hopper design will therefore comprise ... 

A sieve-and-valve tray (Fig. 6.5d) contains a combination of venturi valves and sieve clusters in alternate rows. This tray has a low pressure drop while maintaining turndown equivalent to most valve trays (37, 38). 

Plug Cocks These valves (Fig. 10-152) are limited to temperatures below 260°C (500°F) since differential expansion between the plug and the body results in seizure. The size and shape of the port divide these valves into different types. In order of increasing cost they are short venturi, reduced rectangular port long venturi, reduced rec taugular port full rectangular port and full round port. 

FIG. 17-60 Reverse-pulse fahric filter (a) filter cylinders (h) wire retainers (c) collars (d) tube sheet (e) venturi nozzle (f) nozzle or orifice (g) solenoid valve (h) timer (/) air manifold (k) collector housing (/) inlet (m) hopper (n) airlock (o) iipperplenum, (Mikropul Division, US. Filter Coip.)... 

Fig. 3.3 1-3 Cooling Tower Water (. hloriuiiiiuu Basin water u- circulated by the pump throitgi the venturi at 3t> gpm. Chlorine gas, piiivulril ir. a ton tank, is reduced to zero pressure ni tr.e /r.. s snj c reducing valve to be brought in - < llie u. /-...

This sonic velocity occurs in a pipe system in a restricted area (for example, valve, orifice, venturi) or at the outlet end of pipe (open-ended), as long as the upstream pressure is high enough. The physical properties in the above equations are at the point of maximum velocity. 

For valve trays the effects observed only for the venturi (low dry pressure drop) valve. 

Note In Table 8-22 for Ry, the flat orifice refers to a rectangular design valve and the venturi refers to a circular style valve. 

Valve type Flat oriHce, Rvw Venturi orifice, Rvw... 

Venturi Tube or Flow Nozzle Self-Contained Regulating Valve 0- - Computer Set... 

In this chapter we will illustrate and analyze some of the more common methods for measuring flow rate in conduits, including the pitot tube, venturi, nozzle, and orifice meters. This is by no means intended to be a comprehensive or exhaustive treatment, however, as there are a great many other devices in use for measuring flow rate, such as turbine, vane, Coriolis, ultrasonic, and magnetic flow meters, just to name a few. The examples considered here demonstrate the application of the fundamental conservation principles to the analysis of several of the most common devices. We also consider control valves in this chapter, because they are frequently employed in conjunction with the measurement of flow rate to provide a means of controlling flow. 

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