[TheForge] Power hammer questions

[Jerry Frost]

>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.