PSC Top Detainable Deficiency - E/R Fire Dampers

A Vital Safety Function in case of E/R Fire. 

As we are all aware that one of critical firefighting related safety equipment on board the vessel is E/R Fire Flaps/Dampers. They are mostly operated/tested on weekly basis by responsible Engineers in order to ensure their effective and reliable operation.

 A considerable amount of vessels has been detaining by PSC’s due to defective, and inoperational E/R Fire Dampers.

Not because they always keep the 1st or 2nd place in PSC Top Detainable Deficiency List, Fire dampers should be in good working condition since they have a vital safety function in case of E/R fire.

In the light of their importance, a detailed survey conducted on board our vessel on E/R Fire Dampers. 

Following facts observed;

? Considerable control air leakages 

? Unreliable operation of Pneumatic Cylinders 

The decision has been taken for dismantling, cleaning, inspection, and overhauling of all Fire Dampers.

Pneumatic Cylinders are exposed to the corrosive marine environment due to the vast amount of fresh air drawn by E/R Vent Fans to Engine Room through Fan Rooms. Their anodized aluminum cylinder barrels and end covers might be heavily corroded just after a few years of operation. 

E/R Ventilation system consist of 4 pcs of Vent Fan equipped with Pneumatic Cylinder actuated Fire Dampers.

4 pcs of Pneumatic Cylinders formerly repaired by soft patches were observed inoperable due to excessive air leakage through their End Covers. 

After dismantling of Pneumatic Cylinders, a detailed inspection carried out. Both ends of Pneumatic Cylinder Barrels observed heavily corroded. Roughened surface caused by the eroded material at ends prevent o-rings to serve as a proper sealing agent and causes excessive air leakage.      

Considering Piston’s Effective Stroke in our layout, it has been decided to remove necessary amount of material from Cylinder Barrel both ends in order to have a proper smooth surface for an airtight operation.

The heavily corroded surface at Cylinder Barrel ends removed by Fitter using Lathe machine. After removing corroded material, Cylinder Barrels lost approximately 10-15 mm in length which is inconsiderable for piston’s full stroke and safe operation of complete Fire Damper assembly.

After overhauls, Pneumatic Cylinders have been put back in service without any abnormality.

Traditional Pneumatic Cylinders generally consist of Piston with seals connected to Piston Rod assembled in its Cylinder Barrel which fixed by end covers with tie rods.

1 End Cover 2 Cylinder Barrel 3 Gland 4 Piston 5 Piston Rod 6 Tie Rod

7 O-ring 8 Bronze bearing 9 Throttle 10 O-ring 11 Air Connection

12 Piston Seals 13 Gland Seal 14 Magnetic Band

 ! WARNING!

To ensure that Pneumatic Cylinder is not unexpectedly operated, lock out and tag out power source and compressed air supply before proceeding any work. Failure to follow these precautions could result in bodily injury.

Pneumatic Cylinders Maintenance

A. Inspection

Packings, o-rings, and seals might need periodical replacement, to which the frequency will depend on the operating conditions and cycling.

1- Verification of piston packings

a) Apply air to blind end cap port of cylinder, allowing the piston to travel its full stroke.

b) Disconnect air line from rod end cap port (head) of the cylinder.

c) Apply pressure with your thumb to the open port. Maintain a few seconds and try to feel if air pressure is building up under your thumb. The affirmative would mean that the piston packing is leaking and therefore should be replaced.

d) Repeat steps a), b) and c) to verify the other piston packing. Pressure should be applied to rod end and piston rod should be retracted

2- Verification of rod packings and seals

a) Apply air pressure to rod end port of cylinder

b) Spray a leak-detecting soap solution to piston rod and gland.

c) The formation of bubbles means that the responsible seal or packing has to be replaced.

3- Verification of cylinder barrel seals

a) Apply air pressure to the blind end cap port of the cylinder.

b) Spray a leak-detecting soap solution all around the barrel joint of the blind end cap.

c) The formation of bubbles means there is a leak... Verify if all four tie rods are torqued adequately, according to the makers manual. If leakage persists, the cylinder should be dismantled to rectify the problem. 

B. Repair

Repair of pneumatic cylinders should always be done in a clean area, equipped with adequate tooling. 

1- Dismantling the cylinder 

a) Loosen the tie rod nuts 1/4 turn at a time alternating from corner to corner until the tension is completely relieved on the tie rods.

b) Remove the nuts and tie rods from the cylinder head.

c) Remove cylinder head from the assembly.

d) Remove the piston and piston rod assembly from the barrel.

e) Remove cylinder cap

f) Inspect the barrel internal surface for any scores that could damage the packings. 

g) Remove the gland bushing from the head.

h) Remove packings from both piston and gland bushing, noting the orientation of packing lips. 

i) Clean all parts thoroughly. 

j) Check all parts for excessive wear. Damaged parts should be reconditioned or replaced. 

C. O-ring condition

O-rings and molded parts of elastomers play an important role in sealing technology, both for slowly moving and for static contact points. As a rule, their price is of minor importance, but a failure of this component in Pneumatic Cylinder assemblies causes breakdowns and even complete loss of operability.

Failure of the o-rings might cause Pneumatic Cylinder running jerky and unscheduled downtime will result.

! WARNING

The condition of the o-rings plays a vital role in Pneumatic Cylinder assemblies. To ensure lubrication reliability o-ring condition must be examined properly.

O-rings should be inspected against typical damages;

* Hardening

* Blistering

* Peeling

* Nibbling

* Permanent deformation

* Twisting

* Squeezed o-ring

* Flattened o-ring

Defective o-rings must be discarded and replaced by new ones to ensure lubrication reliability.

! NOTE

While assembling Pneumatic Cylinder, be certain the rubber seals are properly seated in the flanges. Coat these with a light film of grease.