APPLICATION REPORT2611/01/02 E

N • 12/2011

Safety interlocking system, “ACC”

GeneralBecause it is very dangerous to open the capping valve when the digester is under pressure, the valve should have at least two locking systems independent of each other. Thus it is impossible to open the capping valve when the digester pressure exceeds the preset limit, which usually is selected to 0.1 bar (1.45 psi) overpressure.

Figure 1 on the next page shows a standard interlock-ing system of a Metso capping valve.

The primary devices of the system are two separate pressure switches, PS1 and PS2, equipped with hydraulic pressure repeaters. Their preset switch-off pressure is selected to 0.1 bar (1.45 psi) overpres-

sure. The capping valve shown in the scheme is equipped with a pneumatic cylinder actuator, which is operated by solenoid valves V1, V2 and V3. Due to impulse operation, solenoid valves keep their positions also on supply voltage failures. For remote indication for open and closed positions of the cap-ping valve the actuator is equipped with limit switches LSA1 and LSB1. Limit switch LSB2 is used for control of the solenoid valves.

The capping valve, being a self-locking device, re-mains in its last position also at air supply failures.

For local and remote operation/indication the system is equipped with necessary push-buttons and signal lights.

2611/01/02 EN SAFETy iNTErLockiNg SySTEM, “Acc”

2 APPLicATioN rEPorT 12/11

Figure 1. Standard interlocking system

SAFETy iNTErLockiNg SySTEM, “Acc” 2611/01/02 EN

APPLicATioN rEPorT 12/11 3

Figure 2. Standard interlocking system of a Metso capping valve

Figure 3. Mounting plate

The information provided in this bulletin is advisory in nature, and is intended as a guideline only. For specific circumstances and more detailed information, please consult with your local automation expert at Metso.

Metso Automation Inc.Europe, Vanha Porvoontie 229, P.O. Box 304, FI-01301 VANTAA, Finland. Tel. +358 20 483 150. Fax +358 20 483 151North America, 44 Bowditch Drive, P.O. Box 8044, Shrewsbury, MA 01545, USA. Tel. +1 508 852 0200. Fax +1 508 852 8172South America, Av. Independéncia, 2500- Iporanga, 18087-101, Sorocaba-São Paulo Brazil. Tel. +55 15 2102 9700. Fax +55 15 2102 9748/49Asia Pacific, 20 Kallang Avenue, Lobby B, #06-00, PICO Creative Centre, Singapore 339411, Singapore. Tel. +65 6511 1011. Fax +65 6250 0830 China, 19/F, the Exchange Beijing, No. 118, Jianguo Lu Yi, Chaoyang Dist, 100022 Beijing, China. Tel. +86-10-6566-6600. Fax +86-10-6566-2575Middle East, Roundabout 8, Unit AB-07, P.O. Box 17175, Jebel Ali Freezone, Dubai, United Arab Emirates. Tel. +971 4 883 6974. Fax +971 4 883 6836www.metso.com/valves

APPLICATION REPORT

ComponentsThe main components and devices of the interlocking system are:A) Two separate pressure switches with silicon oil filled

repeaters. These units are mounted directly to the valve body with 3” flange connections.

Setpoint of the sensed digester pressure can be as low as 0.1 bar (1.45 psi).

B) Three solenoid valves with a mounting plate with dedicated, ready machined channels for the as-sembly of the solenoids and pneumatic connec-tions to reduce the number of possible leak paths.

The solenoid valve assembly is mounted in a stainless steel enclosure. This control box includes:

❑ Adjustable delay relay ❑ Push buttons for local, manual operation ❑ indication of the control status (man/auto) ❑ Valve position indication ❑ inlet fuse and terminal strips for customer connec-

tionsc) Limit switches at the actuator for open/ close sig-

nals and control of the solenoid valves.

CharacteristicsWhen the digester is under pressure, pressure switch-es PS1 and PS2 prevent the operation of solenoid valves V2, V3 and V1 into a position where the capping valve could be opened. Delay relay d2 cuts off voltage from valve coils V2/2 and V3/2 after adjusted delay time which is normally 20 sec.

Solenoid valve V1 is connected pneumatically in line with solenoid valves V2 and V3. The capping valve cannot be opened unless at least solenoid valves V1 and V2 are in the position shown in the scheme.

Description of operationInitial positioncapping valve open.

Closing of capping valve1. When pressing the button “Manually closed”, coil

2 of solenoid valve V1 is energized and opens the air supply through solenoid valves V1 and V3 to the lower side of the piston in the cylinder actuator. The air pressure closes the capping valve. impulse- operated solenoid valve V1 remains in this position even when coil 2 is de-energized.

When the capping valve is closed, contacts 5-6

of the switch LSB1 close and the red signal light

“closed” shines.2. When overpressure in digester exceeds 0.1 bar

(1.45 psi), contacts c-Nc of pressure switch PS2 open and the capping valve cannot be opened by using solenoid valve V1. At the same time contacts c-Nc of pressure switch PS1 open and contacts c-No close energizing coils 2 of V2 and V3. The air supply to the lower side of the piston is now led via solenoid valves V2 and V3. They remain in this position also in case control voltage disappears.

Interlocking of closed capping valve when digester is under pressure (over 0.1 bar [1.45 psi])1. contacts c-Nc of pressure switch PS2 are open.

consequently, coil 1, which changes position of so-lenoid valve V1, is de-energized and capping valve cannot be opened by using solenoid valve V1.

2. contacts c-No of pressure switch PS1 are closed and coils 2 of solenoid valves V2 and V3 are en-ergized. Delay relay d2 cuts off voltage from coils V2/2 and V3/2 after adjusted delay time which is normally 20 sec. preventing over-heating of coils during cooking period. coils 1 of these solenoid valves cannot be energized until pressure switch PS1 is in position c-Nc. This is possible only when the digester pressure is below 0.1 bar (1.45 psi). Thus relay d2 returns to its original position.

These two interlocking systems, independent of each other, ensure that the capping valve cannot be opened when there is overpressure in digester.

Opening of ball capping valve1. After the pressure in digester has decreased below

0.1 bar (1.45 psi) contacts c-Nc of pressure switch PS2 close and contacts of pressure switch PS1 move from c-No to c-Nc. consequently, coils 1 of solenoid valves V2 and V3 are energized, which allows opening of the capping valve.

2. By pressing the button “Manually open”, coil 1 of solenoid valve V1 is energized and opens the air supply through solenoid valves V1 and V2 to the upper side of the piston in the valve actuator and the capping valve opens.