[TheForge] Frosty's valve set up for air hammer

[Bob Smolen]

Frosty,
Using a single ball valve, my homemade air hammer is now banging pretty
good. In order to get the stroke I wanted , I enlarged the ports from 1/2"
to 3/4 in.
I now want to add a check valve to get the ram to stay up at idle. I dont
follow the second and third circuits you describe in the attached. I do have
a check valve that can be added to the bypass line or wherever needed.
However, this valve will always be one way as it is not a part of the ball
valve as you contemplated in your description. Do you think this will work
or do you need a check valve that is only operational when the valve is open
or idle? If an independent check valve will work in conjunction with the
ball valve, where in the circuit is it placed?
Thanks for your help.
Bob
----- Original Message -----
From: "Jerry Frost" <frosty@customcpu.com>
To: <theforge@mailman.qth.net>
Sent: Saturday, March 22, 2003 5:54 PM
Subject: Re: [TheForge] Power hammer questions


> >The big problem folk seem to be having is the control valving but there's
a
> >very simple system to be found in the Massey pneumatic power hammer,
patent
> ># 707,246.
> have you managed to find an off the shelf valve that will work (and be
> big enough)? What size air passages and valve do you need. an off the
> shelf valve solves the major stumbling block fo rnon machinist types.
>  Geoff
>
> Geoff:
>
> According to Massey the answer is yes. In it's simplest form you could
build
> a self contained power hammer with a single ball valve. You'd lose all but
> the reciprocating action though. I'd start with 1" - 1 1/4" valve and
> airways for a 100 lb hammer but it's a guestimate. I'm NOT an engineer I
can
> do simple arithmatic but that's about it.
>
> Reading the patent text takes some deciphering as it's a British patent
> granted in 1901, the language is 19th century British english legalese so
he
> uses a paragraph or so to say things like, "open the valve and the hammer
> runs." <grin>
>
> Anyway the physics are basic enough. Simply put, the air will take the
path
> of least resistance and all you have to do is direct it where you want it.
>
> I'm going to use the same letter lables Massey uses in his drawings to
help
> avoid confusion for those who download them from the patent server. Which
I
> highly recommend. The only difference being, I'm capitalizing the letters.
>
> His simplest valving scheme goes like this:
>
> Take two double acting pneumatic cylinders, A being the compressor
cylinder
> and B being the ram cylinder.
>
> Connect the tops of A and B with an airway. (H)
>
> Connect the bottoms of A and B with another airway. (I)
>
> Connect the top and bottom of compressor cylinder (A) with an airway (J).
> This is the air bypass and allows air to move freely between the top and
> bottom of the compressor piston (C).
>
> Place a single control valve (K) in the bypass airway (J) and attatch it
to
> your treadle via an appropriate linkage. The valve (K) could be an off the
> shelf ball valve of large enough capacity to allow free flow of air if you
> want.
>
> Okay, here's how it works: While the compressor piston (C) is cycling and
> the valve (K) in the bypass airway (J) is open the air flow moves freely
> between the top and bottom of piston (C). Even though airways (H) and (I)
> are open to the ram piston (F) at all times they are NOT the path of least
> resistance so the ram does not move.
>
> As you depress the treadle the valve (K) in airway (J) restricts the
bypass
> airflow incrimentally making airway (J) no longer the path of least
> resistance. The ram piston (F) is now the path of least resistance and
> begins to cycle with the compressor piston (C).
>
> That's it. The downside though is there's no lifting action at idle, the
> hammer ram will rest on the anvil and if your bypass (J) or valve (K) is
too
> restrictive the ram may bounce when your foot's off the treadle.
>
> The simplest valving scheme I think practical entails the addition of a 1
> way check valve (M) to the control valve (K). The downside of this one is:
I
> really doubt you'll find an off the shelf valve like this.
>
> How this works is pretty slick.
>
> As before when you close the valve (K) the path of least resistance
becomes
> the ram piston and the hammer begins working.
>
> At idle though, the check valve (M) only allows the free flow of air FROM
> the top of the ram piston (F) keeping a vacuum on it. As the compressor
> piston (C) goes down it's top draws a partial vacuum and the check valve
(M)
> prevents it from being relieved by the compressed air from the bottom of
the
> piston (C).
>
> The compressed air from the BOTTOM of the compressor piston (C) takes the
> path of least resistance, airway (I) to the BOTTOM of the ram piston (F)
and
> the ram stays up when your foot's off the treadle.
>
> Flip a lever on the linkage so the valve (K) rotates the opposite
direction
> (180* from it's idle position) and exactly the same thing I described
above
> happens only in reverse, namely the BOTTOM of the ram piston (F) in under
a
> vacuum and it's TOP is under positive pressure. The hammer is now clamping
> against the anvil.
>
> How much clamping force is applied depends on how far you depress the
> treadle. The hammer's BPM depends on how fast your motor cycles the
> compressor piston.
>
> The downside of this scheme is: At idle, if the BPM is too low and/or the
> ram is too heavy it can bleed downward when the compressor piston (C) is
> moving upwards. This is the same action and cause found in the Krause
hammer
> at idle and is no real problem.
>
> The third simplest valve scheme and the one I like the best is just like
the
> last one with a valve (K+M) in the (J) airway and the addition of another
> (K+M) valve in the lower (I) airway. When rotated as above the double
check
> valves prevent any bleed back and the ram will not bleed down no matter
what
> your cycle rate. The second valve can just as well go in the upper airway
> (H).
>
> This third scheme is what we're seeing in Mike Spencer's All Days and
> Onion's hammer valve with the spring loaded check valves in the valve
drum.
>
> Hope that's not too darned confusing. I'd send pics but don't have
software
> that'll convert formats acceptibly. <sigh>
>
> Frosty
> ------------------------
> If it ain't forged
> it ain't real.
> Wrought iron is.
> The FrostWorks
>
> Meadow Lakes, AK.
>
>
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