Regulating pressure head

The arrival of stiff extrusion in the Eirrope in the 1960s - in the USA since 1920 or earlier - also brought the pressure head/die combination with oiling ring. With this system, oil is injected with a pump to improve the sliding behaviour of the clay (Fig. 24). Circa 1970 regulating pressure heads came into use, featuring slides or brakes, which could be externally adjusted and which had an effect on the material flow (Fig. 25). 

Figure 10 is an exploded view of a standard combination pressure head and die assembly of the kind presently in widespread use for the manufacture of common building bricks. It comprises a slide-regulated pressure head and die. The die normally comprises a mounting (or front) plate, a die frame with a wear liner, a slide plate for regulating the column advance, and cores in a corebar. 

The purpose of the regenerated catalyst slide valve is threefold to regulate the flow of regenerated catalyst to the riser, to maintain pressure head in the standpipe, and to protect the regenerator from a flow reversal. Associated with this control and protection is usually a 1 psi to 8 psi (7 Kp to 55 Kp) pressure drop across the valve. 

The apparatus in Figure 38-3, p. 453, is much the same, except that all controls are manual. Close all stopcocks. Pour 500 mL of the more dense liquid into flask A and 500 mL of the less dense liquid into flask B. Start the stirrer and open stopcock A to achieve pressure head equilibritun. Open stopcock B and regulate the flow so that the column will take a minimum of 1.5 hours to fill. 

Fig. 20. Cryostat with electrical control h) bath liquid d) copper vaporizer f) down pipe h) siphon h) condenser 1) liquid nitrogen r) relay Sj) power supply of about 2 volts Sa) power supply of about 18 volts t) vapor pressure thermometer u) pressure head regulator (manostat) v) electromagnetic gas valve the valve plunger must be sufficiently heavy not to stick in its seat.

Pressure heads with/without regulating device, with oil-lubrication, fluidic-optimised, different geometric shapes Dies construction, material... 

Figures 16 and 17 show a hydraulically optimized combination pressure head and die assembly for use in extruding roof-tile slugs. A flexible liner in the pressure head alters the feed contour to regulate the column advance. External control is possible by way of, say, a regulating screw during the ongoing extrusion process. This enables manipulation of the column flow without need of brakes.

Pressurising by use of a pressure raising coil or vaporiser connected between bottom and top of the vacuum-insulated tank. The flow is driven by the difference in hydrostatic pressure heads between liquid in the tank and vapour in the line above the vaporiser, and may be simply controlled by a valve in the vapour line to the top of the tank. Automatic control via a pressure regulator enables the tank ullage pressure to be maintained independently of the rate of liquid removal. 

Figure 3.2 Schenatic diagram of a pressure regulator and mechanical mass flow controller. P, and P are the inlet and outlet pressure of the pressure regulator, respectively. Pj, Pj and P are the inlet, reference, and column head pressure for the flow controller and V is a needle valve used to set Pj to the desired value.

Air from a cylinder at pressures up to about 10 bar (150 psi) is applied to a gas piston that has a relatively large surface area. The gas piston is attached to a hydraulic piston that has a smaller surface area. The pressure applied to the liquid = gas pressure x area of gas piston/area of hydraulic piston. With 10 bar inlet pressure and a 50 1 area ratio, the hydraulic pressure obtained is 500 bar (7500 psi). On the drive stroke, the outlet valve on the pump head is open to the column and the inlet valve closed to the mobile phase reservoir. At the end of the drive stroke, the air in the chamber is vented and air enters on the other side of the gas piston to start the return stroke. On the return stroke the outlet valve closes, the inlet valve opens and the pump head refills with mobile phase. The pump can be started and stopped by operation of a valve fitted between the cylinder regulator and the pump. 

Pressure regulator. The split inlet is back pressure regulated to ensure a constant head pressure, therefore, a steady flow through the column. For capillary columns, the inlet pressure determines the column flow, as per Eq. (14.11). As the inlet operates, the split vent can be opened or closed or upstream gas flow may change the regulator maintains the desired pressure, therefore the desired column flow. 

---