Question

Task 2 (LO 1: 1.2)

Briefly explain the operating sequence of the pneumatic and electro pneumatic circuit diagrams
given below.

S2 Y2 +24V 1 2 3 4 6 7 ε 9 10 11 12 13 14 15 16 S5 HS Oy 軍軍 10

Answer 1

In this, on pressing S8 push button (and not pressing S9), K1 contactor will pick i.e 24V will reach across its terminals. As soon as K1 contactor picks, Normally open (NO) contact of K1 in 2 changes to Normally Closed (NC) position and thus K1 contactor gets continuous supply and it remains in picked position. This Normally open (NO) contact of K1 in 2 is also known as holder of K1 contactor as it keeps the K1 on even after releasing the S8 push button.

Now as K1 contactor is in picked up position, So NO contact in 4 also becomes NC. Thus 24V reaches across K2 contactor (provided K5 contactor and S5 button is not pressed as S5 is NC). When K2 contactor will pick, its NO contact in 14 will change to NC and thus 24V will reach across Y1. Here Y1 is an electro-pneumatic valve. As soon as this valve picks up, air which was earlier entering from position 2 and coming out of position 4 will reverse its direction i.e. air will enter from position 4 and come back from position 2. Thus, it will move the piston towards right hand side. (Such valves are also known as shut off valves which are used in industries to block or allow the movement of gas or water in pipelines). This could also be achieved by simply pressing S7 push button as it would have behaved in a similar fashion as picking up K1.

Similarly on pressing S2 push button (which is an ON push button like S8 and S7), K3 contactor will pick up (get 24V across it) and thus NO contacts of K3 contactor (at 7 and 15) will change to NC. Thus it will remain picked even after releasing the S2 ON push button and valve Y3 will pick up. So, direction of air flow will reverse its direction and piston of Y3 will move to right hand side.

Now, if S4 is pressed and S6 is not pressed then K4 will pick up. Thus NO contact of K4 will change to NC in 10. Now, if S3 is pressed (while K4 is picked), then contactor K5 will pick up i.e. the NO contacts of K5 will become NC in 12 and 13. So, contactor K6 will pick up which will lead to 24V across electro-pneumatic valve Y3 resulting in change in piston position of Y3.

NOTE 1: Here S9 and S6 are stop push buttons which can be used to drop the K1 and K4 contactors respectively i.e.as soon as they are pressed their respective contactors will change from picked up position to normal position.

S3 and S5 are NC push buttons which will change to NO on pressing.

NOTE 2: Here Y3 and Y1 valve can never pick up at the same time as for Y3 valve, K5 contactor should remain in picked condition whereas for Y1, K5 contactor should not be in picked position as its NC contact is used in serie with K2 contactor in

NOTE 3: For the electro-pneumatic valves to operate it is mandatory that there should be proper air pressure in air line 1. This required air pressure depends on the rating of the valve.

NOTE 4: The terminals of contactors across which 24V is to be supplied to pick them are usually labelled as A1 and A2