tailieunhanh - Process Engineering Equipment Handbook Episode 2 Part 2

Tham khảo tài liệu 'process engineering equipment handbook episode 2 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Controls Retrofit C-391 REED rGLASS ENVELOPE FIG. C-414 Reed switch. Source Demag Delaval. FIG. C-415 Single-pole-single-throw SPST reed switch. Source Demag Delaval. FIG. C-416 Single-pole-double-throw SPDT reed switch. Source Demag Delaval. FIG. C-417 Magnetic activation of reed switch. Source Demag Delaval. resistance to the magnetic flux generated from the magnet. This gap resistance decreases as the reed blades come closer together. The magnetic force produced by permanent magnets or electromagnets is inversely proportional to the square of this distance gap. Therefore the reed-switch-blade closure will accelerate as the tips approach each other. The larger the magnetic field the faster the blades snap together. See Fig. C-417. Control Valves A number of process valves are simple hand-turned valves. They include Globe valves Fluid flow through this valve changes direction. Fewer turns are required to move this valve than with a gate valve. It is useful for throttling service. If extremely close regulation is required a needle globe valve should be used. Ball valves require a 90 turn to shut off flow completely. They are much lighter for a given size than either a globe or a gate valve. Maintenance is simple however this valve type is not suitable for throttling. Plug valves can be either lubricated or nonlubricated. They are like ball valves except instead of the ball there is a plug often shaped like a truncated cone. These valves do not seize or gall as might be the case with some gate valves. Diaphragm valves have a flexible diaphragm that closes the pipe against the flow of the liquid. Isolation of the working parts from the fluid stream prevents product contamination and corrosion. Maintenance requires the occasional diaphragm change. Pinch valves are more for laboratory-type application as they stop flow through small-diameter rubber tubing. Some valves operate either manually or automatically. Controls Retrofit C-391 REED rGLASS ENVELOPE FIG. C-414 Reed