Displacement Lubricator No 2

Until recently, I'd been searching for an additional Displacement lubricator to ensure a good oil supply to the steam brake cylinder. The one I already had was earmarked for the Worthington-Simpson Boiler Feed Pump.

As luck would have it, a Cornishman was selling the Worthington-Simpson pump off his traction engine on Ebay. Whilst I didn't need the pump, I noticed in one of the pictures that it had a suitable displacement lubricator on top of it. I enquired as to whether the seller was willing to sell the lubricator on its own and, to cut a long story short, I now have it. (This lubricator, being of the type normally used for a WS pump, will be used for that purpose; the previous one can now be redeployed for steam brake oiling).

When complete, the lubricator is almost identical to the one in the photo below.

Colin Evans's Displacement Lubricator

At first I assumed that there was not much that could be wrong with one of these devices. However, on removing the old viscous oil from it for examination, the central tube was flapping about loosely and obviously not able to perform its function properly. (I've already done a description of how one of these works part way down in 'Why you need a pointy hat' some time ago).

The various bits and pieces are shown below:

Lubricator Internals

Closer examination of the small curved tube shows that its thread has worn over time and, unless screwed in tight, would flap about without making the necessary seal with the valve box.

Tube with its threaded hole in the valve box

Worn thread

Threaded hole to the right in the valve box (or whatever it should be called!)

I cleaned up the tube and thread and screwed them together tightly using Heldite jointing compound to keep them in place.

Reassembled curved tube

So now it should work properly (when reassembled!).

One mystery remains with this lubricator. Most displacement lubricators seem to have a valve for draining condensate to the outside world. This one's drain valve releases the condensate back into the steam and oil connection.

The point of the valve seat is to the right of the bottom of the inlet/outlet hole shown
(same for both valves)

So how does the water get out if there is pressure below? Is it only possible to empty when the system is cold? Or do you just use the drain valve and hope?

Comments welcome!