Answer MEP Question 11

Q. Describe the procedure for overhauling Main Air compressor Valves (Plate type) and explain which parts require close attention. using sketches where necessary. Also, describe the procedure for testing these compressor valves.

 

1. Prior to disassembling and assembling, prepare necessary tools.

- Torques wrench

- Socket wrench

- Hexagon socket

- Screwdriver

- Valve assembling jig

- Suitable box to house overhauled valve parts.

2. Maintenance and Inspection

Air valve: - Remove the valve (1st stage), suction valve (2nd stage) and delivery valve (2nd stage). 

 - Disassembling and reassembling procedure for suction valve (2nd stage) and delivery valve (2nd stage).

 - Remove the valve (1st stage) stuck to the cylinder head by lightly hitting it with the handle of the hammer.

 - Pay attention to the position and state of the valve seat gasket (1st stage) at reassembling.

 - Do not damage the air valve seat. Do not assemble the plate and spring reversely.  When reassembling the valve seat gasket (2nd stage), apply grease to prevent slippage, falling, and air leak.

(A) Entire air valve

- Wipe out the air valve outside (both 1st and 2nd valves) with a clean cloth, and check deposit of carbon or sticking of foreign matters.  Check for sticking of carbon and foreign matter.

- If carbon or foreign matter is stuck, disassemble the valve and carefully clean it with a soft cloth or brush.

(B) Valve plate

- Push the valve plate from the valve seat side using a driver or steel bar (3mm dia.), and check abnormality of valve plate face, and action of spring. Put the driver in several places to check the action of the valve plate. The valve plate will make stroke equivalent to valve lift. Push the valve plate from the valve seat side.

- If the valve plate shows improper action, disassemble and clean it.

- If the valve plate is worn, replace it with a new one.

(C) Spring

- Disassemble the 1st stage side spring to check its damage or wear.

- Check the appearance of the 2nd stage side spring if there is no damage or wear.

- Replace the damaged or worn spring with a new one.

3. Disassemble the valve as follows:-

Before starting disassembling, clean up the surroundings to provide large space and prepare boxes to store the disassembled parts therein.

a. Clean especially around the thread of clamping bolt and nut by removing carbon and dirt accumulated.

b. Apply lube oil onto the cleaned thread

c. Clamp the fixing plate of the jig by vice, then begin disassembling the valve.

d. Place valve on the assembling jig, put holder plate and flat washer on it. Then fix the valve by wing nuts tightened with finger force.

e. Loose valve clamping nut by socket wrench until it can be removed by finger force thereafter.

f. Take out the valve from the assembling jig, then overhaul it in the prepared box.

4. Assembling of the valve:-

a). Check the necessary tools.

b). Apply new oil onto the thread clamping bolt and nut.

c). Place individual valve parts one over another incorrect order. Assemble them by tightening hexagon nut against clamping bolt temporarily with finger force.

d). Check the following:-

    i. Outer face of valve guard and seat to be parallel.

   ii. Retelling of valve guard against seat not to be seen.

  iii. Valve guard to be securely positioned against the seat by knock pin. It can be slightly turned by hand to radial direction within about 5° angle.

  iv. Valve plate should leave freely from the valve seat, i.e make lifting function without any obstruction. Check it by pushing the valve plate with a small screwdriver through the air passage channel of the valve seat.

   v. Place the valve made above mentioned checking on to the assembling jig fix it by tightening wing nuts with finger force.

  vi. Tighten clamping nut with recommended tightening torque by using a torque wrench.

  vii. Take out the valve from the assembling jig. Then check for the free state of the valve plate again. If no defect were found, assembling of the valve is completed at this point.