Valves
COST A diverter valve’s purchase price is only one of many costs you need to consider. Others include shipping, installation, and maintenance costs, material cross- contamination costs associated with internal valve leaks, and lost-production costs caused by maintenance downtime. You can discover these and other performance-related costs by asking for information from users who have installed a particular valve in an application similar to yours.
OPTIONS
Depending on your material characteristics, you can specify that a diverter valve and its components be constructed of cast aluminium, cast iron, stainless steel, or a specialty alloy. And depending on your pneumatic conveying system’s specifi cations and power availability, you can often specify that a valve be actuated manually, by air, or by an electrical motor. You can also specify a valve with an air-controlled solenoid and position indicating switches. Now, keep these selection factors in mind as you explore the types of available diverter valves. The following information covers fi ve common diverter valves: rotary- plug, rotary-blade, fl apper, sliding-blade, and fl exible-tube. Multiple-source, multiple destination diverter valve confi gurations are also discussed.
ROTARY-PLUG DIVERTER VALVE
The housing of a rotary-plug diverter valve (also called a tunnel diverter valve), as shown in Figure 1A, contains a solid rotating plug with a smooth tunnel-like hole bored through it. The material fl ows through the tunnel from an upstream conveying line to one of two downstream lines. To divert fl ow from one downstream line to the other, the plug rotates on a central axis, like a dial, about 150 degrees so that the tunnel’s previous outlet becomes the tunnel’s new inlet and the tunnel’s previous inlet becomes the tunnel’s new outlet to the other downstream line. In another version of this valve, called a parallel-tunnel diverter valve, shown in Figure 1B, two parallel tunnels are bored through the rotating plug. This reduces valve wear, because the plug has to rotate only about 45 degrees to shift the material fl ow from one downstream line to the other. The rotary-plug diverter valve is typically
used for handling pellets rather than powders, because powder can pack between the rotating plug and housing. Shifting the valve “on the fl y” (that is, diverting material fl ow while the conveying system is operating) isn’t recommended, because it can cause the valve’s upstream conveying line to become completely blocked. The valve can be used in dilute-and dense- phase applications and be pressure-rated based on your application needs, typically up to 15 psig for dilute-phase pressure conveying and down to 30 inches mercury for dilute-phase vacuum conveying. Manufacturers can also modify the valve to achieve higher pressure ratings, allowing it to handle abrasive materials in dense- phase high-pressure applications. The rotary- plug diverter valve can have a precision- machined cast housing and heavy pipe fl anges for connecting the valve to the conveying line. The primary
advantages of the rotary-plug diverter valve are its shallow material defl ection angle, which creates a low pressure drop in the pneumatic conveying system, and its ability to handle abrasive materials in high-pressure dense- phase applications. As long as the conveying line is purged before conveying a different material, the rotary-plug diverter valve’s smooth-bore tunnel eliminates material cross- contamination when handling non-dusty granules or pellets. The primary disadvantages of the rotary- plug diverter valve concern it’s cost, susceptibility to seal abrasion, and inability to shift “on the fl y”. This valve usually costs much more than other valves because its precision- machined cast housing is expensive to fabricate, hard to install, and costly to repair. Valve replacement parts are also costly. The rotary-plug diverter valve requires clearance between the housing and sealing
www.solidsandbulk.co.uk Figure 1. Rotary Diverter Valve Illustration
surfaces in order to actuate. Because the valve’s sealing surfaces wear with each plug rotation, material can become packed in the clearance gap and bind the plug, preventing the valve from operating properly. To fi x it, you must remove the valve, clean it out, and replace the seal or housing. Rotary-blade diverter valve - The housing of a rotary-blade diverter valve, as shown in Figure 1C, contains a fl at solid-metal disc that rotates on a central axis to divert material from one downstream conveying line to another. A metal shaft runs through the housing’s centre and lengthwise through the disc, supporting the disc and creating its central axis. An externally mounted actuator connected to the metal shaft triggers the disc’s rotation, and material fl owing from the upstream conveying line hits the disc’s fl at surface and is defl ected into the appropriate downstream line. The rotary-blade diverter valve is typically used for granules and powders, especially in dilute-phase systems, because it’s less subject to powder packing problems than the rotary-plug diverter valve. However, shifting “on the fl y” isn’t recommended because the
valve’s rotating disc can trap material in the sealing areas during the shift. Like the rotary-plug diverter valve, this valve can be used in dilute- and dense- phase systems and be pressure-rated based on your needs, typically up to 15 psig for dilute-phase pressure conveying and down to 30 inches mercury for dilute-phase vacuum conveying. The valve can be modifi ed by the manufacturer to achieve higher pressure ratings so it can handle abrasive materials in dense-phase high-pressure applications. The valve can have a precision- machined cast housing and heavy pipe fl anges for connecting it to the conveying line. The primary advantages of the rotary- blade diverter valve are the same as those of the rotary-plug diverter valve: its shallow material defl ection angle, which creates a low pressure drop in the pneumatic conveying system, and its ability to handle
Solids and Bulk Handling March 2014 39
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52