Saturday, 19 August 2017

Operating Experience (3) Has Beans?

Sentinel 7109 has been back in operation for over a year. At first, it was a matter of getting Joyce working; now I'm becoming aware of oddities that aren't working quite as well as they should.

One of these is a jet of steam below the front engine when working hard uphill. This indicates steam leaking through a piston rod gland in the front engine.
Arrowed jet of steam (Photo: Sean Dudden)
Looking underneath, there are four copper drain pipes pointing downwards immediately to the rear of the front engine.
Four drain pipes
In the photo above, the left end one drains leaks from the front engine's water pump; the second and fourth ones are drains for the four automatic cylinder drain cocks; the third one drains the two piston rod glands. This third one has been getting hot at its tip whereas the others just look a bit oily.

Having been aware of this leak for some time, I made preparations for repacking the left hand steam gland of the front engine. I needed to order the packing material but did not know the size so I loosened the nuts holding the gland packing in place to enable me to gain access to measure the size of the gap to be filled. I was not prepared for what I found.
Beans!
Look closely at the dead centre of the photo. Instead of old packing, I found what looked like a bunch of dark grey baked beans! These I removed for examination.
Beans, Beans
The beans looked to be rolled graphite, the remains of the original packing. It is possible to write with them, hence graphite.

Clearly, I couldn't simply put them back to be ready for the next public steaming, six days away.

Sentinel used to produce packing rings with a part number for ordering. This luxury is not available nowadays so I had to find a current substitute. Stuart Gray (Heritage Steam Supplies (HSS)) advised me that the material needed was Pilotpack 4010.
Empty packing space (rough piston rod surface)
I found it very difficult to measure the distance between the piston rod and the surface of the packing space, known as a stuffing box. However, there is a gland bush which holds the packing in place. This is a close fit in the stuffing box so I measured the thickness of the bush instead.

It measured almost exactly 1/2". Thus 1/2" x 1/2" square section Pilotpack 4010 was what was required. About a yard is required to make the five rings of packing for a 1.35" diameter piston rod.

HSS were out of stock so I had to go directly to the manufacturer, Beldam Crossley, to get it in time. Beldams were more than helpful and sent me eight metres of 4010 next day. Beldams were cheaper than HSS but I had to order eight times as much as was needed immediately. (There are four piston rods in all so it's not that excessive!).

Following instructions provided by HSS, I prepared the required five rings by wrapping and clamping the length of 4010 around a mandrel (piece of plastic pipe the same diameter as the piston rod) then cutting to make each ring using a Stanley knife. The instructions say that each ring should be inserted into the stuffing box so that the ends 'butt' together. Clearly the writer of the instructions has not worked with 4010 as, when cut, the ends splay out like a pony tail. Butting pony tails is not really what is required but for this attempt that is exactly what I had to do.

For the initial attempt at fitting, I could only get four rings into the stuffing box.
Four rings fitted (they were soaked in SCO1000CTRO+ cylinder oil)
I screwed the clamping nuts tight to push the packing home and then slackened them off a turn or so to leave the packing uncompressed. As the piston rod surface is pitted, over-tightening the packing will just lead to it being abraded and failing.

There is some steam leakage as a result but it is better than the stuffing box being left full of beans again!

After the first day running with the new packing, the four rings had survived but were more compacted than when fitted. A gap was thus left so I could fit the fifth ring. Again, I tightened the nuts to push the packing home and then slackened them off a turn or so. Some tweaking will be needed during the next steaming.
Five rings fitted
Working on the packing is not easy physically with everything in situ. However, erecting a seat did make things a little easier.
'In sit you'
Only three more steam glands to go, the right front one could still be guilty...

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