04-13-2014, 01:15 PM
At about 2:26 on this video you see and hear a Y6b starting <!-- m --><a class="postlink" href="https://www.youtube.com/watch?v=LF-6FKD0pr0">https://www.youtube.com/watch?v=LF-6FKD0pr0</a><!-- m --> It is a single loco in helper service, and I'm pretty sure you're hearing 8 exhausts per revolution of the wheels.
EDIT: there's a sequence taken from the top of the smokebox just ahead of the stack, and you can pretty clearly hear exhausts coming from two sets of cylinders, audibly different. The N&W apparently approved and supervised these shots, by the way.
The producer says this is actual sound recorded with the video.
ANOTHR EDIT: This site <!-- m --><a class="postlink" href="http://locodriver.co.uk/Vol05/Part09/02/index.html">http://locodriver.co.uk/Vol05/Part09/02/index.html</a><!-- m --> says "The N&W Mallets were provided with a simp[l]ing valve, enabling them to operate as four cylinder simple expansion locomotives. At starting, the exhaust from the high pressure (HP) cylinders was taken directly to the blastpipe, instead of to the low pressure (LP) cylinders as normal. This eliminated back pressure on the HP pistons at starting and meant an increase in tractive effort." Also, the Wikipedia entry on compounding says, "The eternal problem with compounds is starting: for all cylinders to take their weight, it is advisable to have some way of short-circuiting the HP cylinders and getting steam at a reduced pressure directly to the LP cylinder(s); hence many of the patented compound systems are associated with particular starting arrangements." I have a feeling that simpling valves were common on Mallets.
If you search Y6b on Youtube, you can come up with quite a lot of clips of these locos. One question is whether the sound is dubbed, so you can't necessarily trust them. On the other hand, at any apprecialble speed, the chuffs blend into a roar and the individual beats are harder to discern.
EDIT: there's a sequence taken from the top of the smokebox just ahead of the stack, and you can pretty clearly hear exhausts coming from two sets of cylinders, audibly different. The N&W apparently approved and supervised these shots, by the way.
The producer says this is actual sound recorded with the video.
ANOTHR EDIT: This site <!-- m --><a class="postlink" href="http://locodriver.co.uk/Vol05/Part09/02/index.html">http://locodriver.co.uk/Vol05/Part09/02/index.html</a><!-- m --> says "The N&W Mallets were provided with a simp[l]ing valve, enabling them to operate as four cylinder simple expansion locomotives. At starting, the exhaust from the high pressure (HP) cylinders was taken directly to the blastpipe, instead of to the low pressure (LP) cylinders as normal. This eliminated back pressure on the HP pistons at starting and meant an increase in tractive effort." Also, the Wikipedia entry on compounding says, "The eternal problem with compounds is starting: for all cylinders to take their weight, it is advisable to have some way of short-circuiting the HP cylinders and getting steam at a reduced pressure directly to the LP cylinder(s); hence many of the patented compound systems are associated with particular starting arrangements." I have a feeling that simpling valves were common on Mallets.
If you search Y6b on Youtube, you can come up with quite a lot of clips of these locos. One question is whether the sound is dubbed, so you can't necessarily trust them. On the other hand, at any apprecialble speed, the chuffs blend into a roar and the individual beats are harder to discern.