Hi my name's Dave and welcome to my YouTube channel. First of all welcome to
all the new subscribers and we have many of them and I would first like to thank
everybody, there was quite a few people involved they made considerable effort
to put the word out and get our subscriber numbers up and a certain
channel that many of you know of Alex a 2strokestuffing and thank you one and
all for that, we've made the numbers that we need we've retained the YouTube
Partner Program unfortunately YouTube has made a bit of a mistake about the
numbers and now states that they took the numbers from some days prior so
monetization is off the menu for now we'll get it back in some months maybe
but anyway I don't want to want to talk about that because it just infuriates me
a bit so we'll get straight on to it. For anyone not familiar with the channel
what we do here is straight technical lectures on all of the fundamentals and
scientific operation of engines at the moment we're doing two strokes, and we're
doing two stroke expansion chambers specifically. Now I've been doing a lot
of videos on expansion chambers and it's getting a little bit labored and we will
get back to that, in the meantime I thought we'd just jump to something else
just to mix things up a little bit and this is a fairly common topic nature of
video which is the reed valve intake system versus the rotary disc valve
intake system, now you may have seen a number of videos on this topic which
briefly cover them and gives you rough comparisons of the of the power
characteristics of the reed valve intake and rotary disc intake but it
doesn't go into too much detail. On the outset I can tell you that with a
with a rotary disk intake and a reed valve intake it's not
really a matter of comparisons between one or the other so it's not really fair
to compare them to each other one has a distinctive benefit
in one condition and the other one has a benefit in the different condition and
the short of that is is that the smaller capacity that an engine is the more
benefit a rotary disc intake will be so from engines generally from 150 CC per
cylinder downwards the rotary disc has more, and more advantage
when you get down to 100cc and below hundred CC the rotary disc intake has a
clear advantage over the reed. Why is it in a smaller engine that it's more
desirable than a larger engine ? well that comes down to the gas inertia in a very
large capacity engine. There is very large volumes of gas that
run through the ports and the larger that is and the bigger
capacity of the engine the less propensity there is for for any
reversion effects, in other words if the pressure differential changes it's
more difficult for a large volume of gas to slow down and revert backwards but in
a small engine that becomes more and more issue so in other words a very small flow
of inertia of gas can can reverse very quickly and so the benefit
of the rotary disc valve intake being able to control its intake is is more
suitable to smaller engines because they suffer that problem more and more so the
smaller the capacity of the engine is the more it can suffer a back flow of
the gasses because it hasn't got as much gas volume and that's inertia and
so the rotary disc will be an advantage to smaller and smaller engines
because of that reason. Keeping in mind that at all times
gas will always try to equalize to pressure differentials so if a pressure
in a crank case for example drops below the pressure in the cylinder then the
gas will attempt to backflow back down the transfer and likewise in the other
direction, where the rotary disc comes into this is that if we look at the
timing down here and we can see the difference between
the piston portal engine a rotary disc valve engine a reed valve engine at high
and low rpms and you'll see, noting the intake open and intake closed periods
here on the piston port are symmetrical because it's controlled by the piston,
whereas the rotary disc valve opens very very early and the disc
valve closes around the same time as the piston port the reed valve at low engine
speed very much mirrors what a disc valve looks like at low engine speed
with a reed valve open here reed valve closed here at higher speeds it starts
to become more symmetrical like the piston port and that's kind of
contrary to what you would really want in an engine, but nevertheless the
problem with reversion to begin with with the the rotary disc is
you'll note on the piston port the inlet actually opens sometime after the
transfer and exhaust closes now keeping in mind that what we've got there is a
situation where the piston is rising and the pressure inside our casing down
below is reducing now what we can get is we can get a reversion of gases that
basically back flows back down the transfer, then again forward flow
but the disc valve basically does it by opening the disk valve very early and if
we open disc valve very early and then we get a pressure drop in the crankcase
instead of the pressure attempting to equalize as it does with the piston port
back through the transfer, the inlet to the case from the carburetor is open
so that it can actually equalize air through the carburetor which is more
desirable than a back flowing down the transfer. So opening the rotary disc
valve early alleviates that, now there's a bit more detail to it with the
relationship of the disc valve opening to the transfer closing okay, in a
high-powered engine we want the disc valve to open
some degrees before the transfer closes and then in a engine we want very
broad power then the disc will open almost around the same time as the
transfer closes, now another benefit of the rotary disc is that we
can determine where our rotary disc valve opens or our intake opens to
the casing and then we can fix that point to get the desired effect the
distance between transfer closing and dis valve open, and then if we want to
increase the total timing we can just modify the disc valve closing period so we
have a little bit of latitude as you can see. At high speed the reed
valve closes quite a bit later so what we can do is we can actually fix this
point and then we can increase our total timing period by just closing the disc
valve a little bit later or a little bit earlier depending whether we want a
lesser amount of timing so the total degrees is from DVO to DVC. So far we've
dealt with the issues of backflow reversion whatever you like to call it, and most
of those issues are low speed mid range issues so the rotary disc kind of
wins that race is because the reed valve always constitutes a pressure
differential between each side of the reed valve the carburetor side and the
inside so for ultimate high-speed flow the rotary disc valve is
unobstructed and basically it wins the race at that point for the high end so
it's got the benefits of early opening and the adjustment of the relationship
between DVO and TC and we can adjust the timing and all that deals with the
low-end and mid-range but at the top end it just comes down to restriction of the
flow and that's where the rotary disc has the other edge on that. If you want
me to elaborate more on the design factors of reeds and rotary disc
we can get into that later, if you'd like that please mention in the comments
section, it's a little bit deep down the rabbit hole I'm not sure if it justifies
the video at this stage but if you want to know by all means ask.
But time wise I think that will
about do it. I think you can only take so much of
this at one time and I hope you found that informative, if you have any
questions at all please hit the comment section and ask. So I'd just like to say
thank you again for everyone coming on board and subscribing and supporting the
channel I really really appreciate, it it's just it's injected a bit of a new
life into into things and I've got some some new ideas about videos to do and
hopefully when things turn around we will be able to afford to do a little
bit of actual simulation of engines by building some equipment so that we can
do some visual displays of some of this stuff which I'd like to get onto later I
have a complete machine shop etc so I can do that here. And yes that will do it
for today so again thanks for coming and watching the videos, thanks for your
subscription and hopefully we'll see you in the next video. Bye for now