The Thornton Pickard Roller Blind Shutter is one of the earliest examples of what is now referred to as the focal plane shutter. Unlike the later (and more complex) Graflex style shutter, these were made to be used in front of or just behind the lens and were sold as a complete unit that could be retrofitted to an existing camera. They came in a variety of sizes and were sold for around thirty years. There were even Japanese made versions with steel casings instead of the usual mahogany. They are relatively simple units and the main problem encountered with them is curtains that are either broken or leak light, unsurprising in a unit that may will be at least 80 years old and may well be closer to 100. Fortunately it is relatively easy to replace the curtain and get the shutter working again.
The shutter consists of a cloth curtain with a rectangular hole in it that is attached to two brass axles. The axle on the right is hollow and has another axle inside which is attached to the outer axle by a long coil spring. The tension on the spring can be adjusted by winding a brass knob on the top and the shutter speed is indicated on a dial at the bottom. The axle on the left is solid and has a pulley and a cog at the top. The cog connects to another cog which has a racthet mechanism to allow the shutter to be held in place. The pulley has a string wound around it that runs across the shutter and out of the right hand side.
When you pull the string it turns the pulley, which in turn winds the shutter curtain on to the left hand axle. As the curtain is unwound from the right hand axle this motion winds up the internal spring in the axle. The ratchet stop on the large cog on top is held in place by the long lever. Lifting the lever releases the cog and the spring unwinds, which in turn pulls the curtain back onto the sprung axle. As the curtain moves, the hole in it moves past the aperture in the shutter casing and light passes through. The curtain completes it movement and the aperture is blocked again.
That's not all. The designers placed another stop on the gear so that the shutter could be held open as well. If you moved the lever over to the "Time" position the first time you fired the shutter it would stop with the aperture open and then firing it again would close it. In the picture above you can see a small hole in the lever. This can be threaded for a conventional cable (or air bulb) release to be attached. Also note the brass knob on the right. This is connected to the inner axle and turning it tensions the shutter and thereby increase its speed. The spring next to it is another ratchet mechanism, preventing the shutter losing all of that tension.
Here is another style of cable release. Pressing the plunger pushes the cable out which lifts the little brass hinge which in turn lifts the lever and fires the shutter.
Another view of the cable release. Due to a shortage of space there is no nice celluloid disk with "Time" and Inst". This version of the shutter only has "T" and "I" stamped into the plate that holds the sprung axle in place.