What is a 'Spring and Loop' action?

[IvorYtickler]

I've been reading about the dreaded S&L and must confess I'm not sure I understand what it is.
My own rather mediocre grand piano has a short fabric loop connected to a wire spring as part of the action.... so does this make it spring and loop? Is there a diagram anywhere that I could compare against my piano's action?

[Gill the Piano]

Yours is a SIMPLEX action; it was cheaper to make than the conventional roller action. If you google these terms under 'images', you may find a diagram. Bill on the History section of this forum has an excellent collection of action diagrams. The term 'spring & loop' is more usually applied to an upright action from the mid/late 19th century.
You'll find the techs tend not to like the simplex grand action, but as long as the loops stay intact, they work all right. Repairing the loops is fiddly but not difficult.

[Barrie Heaton]

You don't need to g it's all on the UK Pinao Page
http://www.uk-piano.org/herrburgerbrooks/index.html

[vernon]

upright spring and loops(Costas) are to be avoided at all costs,literally.
Simplex grand actions,as the delightful Gill the Piano points out, work ok.

[vernon]

As a matter of historical intest,I think you must be referring to the old established firm of Sprink und Lopp of Kleinescheithaus, Lower Saxony.(see Bill Kibby, Piano History)
They specialised in fine actions made solely of wrought iron and brass and palm tree fronds.
These gave a very positive response though rather metallic in effect, and a certain hollowness of the coconuts.
Herr Sprink,the founder, was especially interested in the harmonic effects of hammers made with the wool of pregnant yaks. After many years this experiment was discontinued due to the imposition of chinese hegemony over the Dalai Lama's furry products, and a vow of celibacy on behalf of the aforemention bovines.
Herr Lopp,having denied any inappropriate relationship with Herr Sprink in the key bushing workshop in Kleinesscheithaus in December 1924 ,(viz reports Lower Saxony Court Reports 1923 Sexual Maniacs et al und Kleinesscheithaus) continued to develop his revolutionary ceramic action built solely of arts trouvee and the detritus of the local abbatoir and tea cups. He was in the forefront, with Frau Bechstein, of the growth of the German National Party party headed by Corporal Hitler who accorded him the" Honour of Grosshero der Staat und Kleinescheithaus" He later had him shot.
Examples of his work are in much deand today and often command fouble digures

[PianoGuy]

upright spring and loops(Costas) are to be avoided at all costs,literally.

I dunno? They're infinitely better than Starbucks, but not a patch on a decent Lavazza or Illy admittedly.

[IvorYtickler]

On closer inspection I noticed that the action is a Schwander, so the diagram on that page looks spot on.
What are the potential issues with this action?
There is currently one key which can jam occasionally, the hammer seeming to 'stall' and get stuck when played hard and repeatedly. Could this indicate a problem with a spring. Or, indeed, a loop?