High performance valves

Some manufacturers have special designs for particular applications, but high-performance valves extend the characteristics of the normal API/ASME/PED and EN requirements. Many are resilient-seated design. 

Opening and closing tolerances too short 1. Change valve trim and retest. 2. Use high performance valve. 

Butterfly and diaphragm valves are other options. Butterfly valves can be lined with an elastomer or a fluorocarbon resin. Soft-seated, high-performance valves have higher pressure ratings but allow contact of the process fluid with the metal. 

To provide isolation, use a separate on-off valve and avoid the specificatiott of tight shutoff and high performance valves for throttling reagent. 

Reciprocating pumps are those most commonly used in high performance Ic. The single-piston type usually has inlet and outlet check valves with some mechanism such as variable stroke frequency to minimize the effect of pump pulsations. Dual-piston pumps operate with the pistons 180° out of phase to minimize pulsations. For this system to work optimally, the piston units must be identical. 

A high-performance biitterllv valve has a disc that is offset from the shaft center line. This eccentricity causes the seating surface to move avv av from the seal once the disc is out of the closed position, reducing friction and seal vv ear. Also Icnovvn as an eccentric disc valve, its advantage is improved shutoff vvliile maintaining high ultimate capacity at a... 

Applications include high-performance insulation for wire and cables (particularly heater cables), and corrosion-resistant linings for pumps, valves, pipes and other chemical equipment. Its availability in the form of film and tubing has led to its demand for both corrosion protection and antistick applications. 

Figure 8-71 A. Nutter MVO high performance fixed valve tray with 4 1 turndown ratio. Used in new installations and to replace sieve trays. Used by permission, Nutter Engineering, Harsco Corp., Bui. CN-4.

High Performance Liquid Chromatography. All separations were performed using an Altex Scientific (1780 Fourth Street, Berkeley, CA 94710) Model 320 Advance Research Chromatograph, consisting of a model lOOA dual piston analytical pump, a Model 153 UV detector, a Model 210 injection valve, and a Model 155 recorder. The columns (600 x7.5mm) evaluated were the Spherogel TSK-SW-2000 and SW-3000 (Altex). Unless otherwise stated, all separations were carried out at 23 - 25 . 

Piston rods in a conventional high performance instrument typically are driven by a cam. The cam smooths the delivery of the mobile phase. Dual pistons allow one cylinder to recharge while compression of the other maintains the operating pressure. More recently, electronic flow sensing has been used to continuously adjust and maintain control of the flow rate. Check valves ensure that flow is unidirectional, as well preventing a drop in pressure during the recharge cycle. 

Apparatus Pumping systems used in these studies for high-performance columns were a Varian 8500 syringe pump and a Varian 5000 isocratic pump. An Altex IlOA was employed for the con-trolled-pore glass (CPG) columns. Waters Associates model 401 refractometers were used on all instruments. Stagnant mobile phase was kept in the reference side of the refractometer. Samples were injected with a Rheodyne 70-10 injection valve using a 20yl loop (lOOyl for CPG columns). 

Fig. 6.1.4 Components of the high-performance liquid chromatography (HPLC) system for oxidized pterins with column switching. The autosampler starts the chromatography software, which controls valves and pumps. Pump 3 is used only for rinsing the precolumn. Details of the three valves and their different positions are explained in Fig. 6.1.5...

In most common turbulent-flow chromatography experiments, a second conventional high-performance liquid chromatography (HPLC) column is employed. The conventional HPLC column, usually referred to as the analytical column, is used for peak sharpening and additional separation prior to MS detection. This approach requires an additional valve and pump to control the final HPLC separation. A typical dual-column methodology is shown in Fig. 10.5. 

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