Nonreturn valve

A smear head causes less stagnation and overpacking than a nonreturn valve. A conventional-type reverse-tapered nozzle with the bore as large as possible without sudden changes in diameter is preferred. Independently controlled, zone-type heaters for heating the nozzle and at least two zones on the cylinder are used. 

Steam Purity. Boiler water soHds carried over with steam form deposits in nonreturn valves, superheaters, and turbine stop and control valves. Carryover can contaminate process streams and affect product quaHty. Deposition in superheaters can lead to failure due to overheating and corrosion, as shown in Figure 6. 

All respiratory protective systems should be stored in clean, dry conditions but be readily accessible. They should be inspected and cleaned regularly, with particular attention to facepiece seals, nonreturn valves, harnesses etc. Issue on a personal basis is essential for regular use otherwise the equipment should be returned to a central position. Records are required of location, date of issue, estimated duration of use of canisters etc. 

Valve Arrangement of Auxiliary Feedwater System and Main Steam System during Shutdown - the auxiliary feedwater system has six MO Vs in the flow path to the steam generators and the main steam nonreturn valves are normally closed during shutdown. These valves depend on offsite power and are difficult to manually open. 

The relief valve was sized on the assumption that two nonreturn valves in series would prevent backflow Into the vessel. 

Both nonreturn valves corroded, allowing back-flow to take place. 

Backflow from the delivery side of the pump was prevented by a check (nonreturn) valve. In addition, a control valve and a hand valve well away from the fire were closed (Figure 7-5). 

The control valve in the delivery line to the furnace was also closed. Unfortunately, this valve was bypassed by the line through the heat exchanger. In the heat of the moment, no one remembered to close the valve in the bypass line. In addition, the check (nonreturn) valve did not hold. The return flow of oil from the furnace was stopped by closing a hand valve next to the furnace, which was about 30 m from the fire. Afterward, another EIV was installed in the pump delivery line. 

Figure 14-2. The check valves (nonreturn valves NRV) prevented a leak test of the equipment to the left of them. During startup a leak occurred at the point indicated.

Reflux drum Mixer or stirrer Breathing apparatus (BA) Slip-plate Refrigeration plant Knock-on (or domino effects) Nonreturn valve Blinded... 

Presence of safety devices (e.g., nonreturn valves, remotely operated isolation valves)... 

A tabulated form as in Table 19.3. This shows flows versus pipe length and diameter for both copper and steel. Such tables are included in British Gas lM/16 and British Standard BS 6891. Note that Table 19.3 includes allowances for elbows, tees and bends. Allowances, equivalent to numbers of pipe diameters, must be made for all pipe fittings, which cause an additional pressure loss. Further details for allowances to be made for pipefittings, including valves and nonreturn valves, are given in Table 19.4. 

Water tube boilers have a pressure gauge, vent cock, and drum safety valve on the top of the steam drum. Where superheaters are fitted, the steam takeoff line leads to the superheater, which is followed by a superheater safety valve, automatic nonreturn valve, and stop valve with a pressure-equalizing line and valve. 

Apart from the BD valves and drain valves, a boiler is fitted with a safety valve (at least one), stop valves, and (usually) automatic nonreturn valves. As a minimum, these valves must be dismantled, inspected, and overhauled annually. 

Auxiliaries are additional boiler fittings that provide controls for ease of operation. They may include additional valves (such as check valves on feed lines, nonreturn valves on steam distribution lines, and the various boiler system drain valves), gauges, connections, and devices to regulate FW, air, and fuel and to provide for the efficient production, pressure, temperature, quality, and flow of HTHW or steam. 

The actual cylinders and pistons of a two-headed pump are constructed in a very similar manner to the single piston pump with a sapphire piston and a stainless steel cylinder. Each cylinder is fitted with nonreturn valves both at the inlet and outlet. The cams that drive the two pistons are carefully cut to provide an increase in flow from one pump while the other pump is being filled to compensate for the loss of delivery during the refill process and thus, a fall in pressure. A diagram of a twin-headed pump is shown in figure 10. 

The plasticator on an injection-molding machine is a specialized plasticating single-screw extruder. The plasticator has two main differences there is a nonreturn valve on the tip of the screw, and the screw retracts as molten material accumulates between the nonreturn valve and the end of the barrel. Pressure is maintained on the accumulated material by a constant force applied to the shank of the screw via the drive system. This force is typically measured as a pressure applied to the shank and is referred to as the back pressure. During the injection step of the process, the screw is forced forward, the nonreturn valve closes, and the material is injected into the mold. Additional information on the injection-molding process can be obtained elsewhere [Ij. 

Figure 10.34 Schematics of a poppet-style nonreturn valve a) full view, and b) a cutaway view showing the flow paths for the poppet valve in the closed position. The poppet valve is forced forward during plastication to allow flow from the screw channels to the tip. The poppet is forced back during the injection step, preventing polymer from flowing back into the screw channels (QSO valve schematic courtesy of Jeffrey A. Kuhman of Glycon Corporation)...

The injection-molding press was producing a part and runner system that had a mass of 2.15 kg. The mass was plasticated using a 120 mm diameter, 8L/D screw. The screw used for the process had a barrier melting section that extended to the end of the screw, as shown by the specifications in Table 11.9. That is, the screw did not have a metering channel. Instead, the last sections of the barrier section were required to produce the pressure that was needed to flow the resin through the nonreturn valve and into the front of the screw. The specific rotational flow rate for the screw for the IRPS resin was calculated at 9.3 kg/(h-rpm) based on the depth of the channel at the end of the transition section. The screw was built with an extremely low compression ratio and compression rate of 1.5 and 0.0013, respectively. For IRPS resins and other PS resins, screws with low compression ratios and compression rates tend to operate partially filled. The compression ratio and compression rate for the screw are preferred to be around 3.0 and 0.0035, respectively. The flight radii on the screw were extremely small at about 0.2 times the channel depth. For IRPS resin, the ratio of the radii to the channel depth should be about 1. 

As discussed in Section 11.12.2, several root causes exist for black streak contamination in molded parts. These root causes include degradation of the resin in the screw channels and nonreturn valve or runner system, degraded material entering with the resin feedstock, and poorly dispersed pigments in the color masterbatch. To determine if the color concentrate masterbatch was the source of the black streaks, the color concentrate was removed from the feedstock and only natural... 

All drains should have deep seal traps to avoid back-flow (nonreturn valves). 

When the dispersed phase, usually but not necessarily the cells, is of interest, no separation of phases need take place during sampling. The system must be opened in such a way that no infections can enter the reaction space either during sampling or between the sampling events. This requires the use of nonreturn valves and probably some repetitive sterilization procedure of the valve and exit line(s), as depicted in Fig. 18. 

The dog is placed on an undersheet and its head is secured by an assistant. The upper and lower jaws are separated by exerting pressure on the Ups with both hands. The stomach tube moistened with mains water is introduced into the open throat. Caution do not introduce the tube in the trachea. Pour mains water into the glass funnel fitted on the stomach tube over the nonreturn valve to check that the tube is correctly positioned. If outflow difficulties occur, adjust the position of the tube by moving it slightly backwards and forwards. Then introduce the test substance to be administered. Then rinse the tube and remove. 

Self-draining voive Chain operated voive Reel voive Quench voive Needle or V-port valve Angle nonreturn valve... 

Most thermoplastic processes utilized for HIPS applications use a single screw to melt and pressurize the polymer. Screw extruders in industry used with HIPS can have screw diameters from 20 to 200 mm and can melt process over 2000 kg/h. Two-stage, vented screw designs are predominantly used for extrusion of HIPS, whereas single-stage reciprocating screws, with a nonreturn valve, are common in the HIPS injection molding process. 

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