s for the lower valve seat.
PPCo Plastic seat - PPCo uses an injection molded lower valve seat in the valves that they
make. This seat is well made and accurate but extends up high above the floor of the valve
block chamber limiting the room available for the stem assembly. They do not use an
adjustable valve disk in their valves so they do not need as much space as the adjustable
assembly requires. This valve seat is not in their catalog but generally they will sell a set to
you if you call. I did not try this valve seat since I wanted to use the original Wurlitzer
adjustable valve travel design.
Plastic
PPCo
Grommet
Brass
Bakelite
Lower Valve Seats
PPCo
Stainless Steel
Upper
Valve Seat
Canvas Grommet seat - Perhaps the most popular choice for the lower valve seat is one of
the brass rope grommets that are used for rope hold-downs in canvas tarps. Originally I had
planned to use these grommets but after doing some tests, I opted to use the Bakelite lower
seat instead. I tested several suppliers of the brass grommets and with some effort and
watch-outs, they can be made to give satisfactory results. Not all suppliers products are
created equal. Some are solid brass and are preferred. Some are brass plated steel and are
to be avoided.
Some grommets do not provide a flat
uniform surface and therefore do not
seat and seal well. In fact they can fail
miserably. As a quick check, rub one
of the grommet faces a few times on a
sheet of very fine emery paper glued to
a flat surface. Look at the area
polished into the surface to make sure
that you see a uniform donut shaped
area with no breaks.
Surface Not Flat
Uniform donut for
uniform flat surface
Diameter
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Last Revision 1/31/07
Page 1 I used blue layout fluid on the grommets above, so that these polished areas would show up
better. One other issue to consider when using the grommet is the larger effective diameter
of the Grommet seat which can limit the pull-down effect of the lower valve leather and
increase leakage, particularly if the lower leather is not glued right on the edge. I measured
the leakage of the lower valve seat using a flow meter and the valve leakage could increase
by as much as 50% if the valve stem was not centered on the valve seat. It may be possible
to increase the diameter of the lower fiber disk to help but I did not try this.
Some of the grommets narrow
considerably at the neck and need to be
trimmed. This section of the grommet
needs to be ground away, down to the
straight walled section of the the grommet
opening. Also, you will have to make
sure there are no burrs to catch the fluted
stem. The valve floor will have to be
counter-sunk so that the grommet will
seat on the floor of the valve chamber.
Brass Tubing seat - A short section of brass tubing press fit and sealed in the valve block
makes a very good lower seat. The leather facing end needs to have a radius to mate with
the leather facing and all burrs need to be removed from the other end. These are easier to
make if you have a metal lathe, using a cut-off tool to cut short sections of equal length, and a
lathe tool with a radius ground in it to make the radius.
Bakelite Tubing seat - Original Wurlitzer lower valve seats were made of Bakelite which
historically was one of the earliest plastics used. Todays version of Bakelite, or Phenolic
goes by the trade name Garolite. Valve seats made from a Garolite tube are made with the
same process as used for the brass tubing. The advantage of using a Garolite tube is that a
small wood lathe could be used to make them. Unfortunately my little wood lathes spindle
hole was not large enough to feed the Bakelite tubing through and I did not want the waste of
cutting a bunch of short sections. I had already made a cutting tool for my wood lathe before
I found this out. I ended up using the tool anyway on my metal lathe.
Radius
Cutting
Cut-off
Section
Length
Gauge
bobhumes@aol.com
Last Revision 1/31/07
Page 2 It doesnt take much to machine Bakelite. I made this tool out of unhardened drill rod. It
includes a place on the side with a small radius ground in it for the face radius and a straight
section to act as a cut-off tool. I fastened a short piece of brass to the side to act as a gauge
to make the height of each seat the same. Since all lathe operations were consolidated in
this one tool, I could make the seats on a production basis, cutting the radius and then cutting
the tube and starting again.
I pressed the lower seats
into the block with a piece
of �" diameter Bakelite
tubing. I cut a shoulder
on the inside of the tube
1/16" deep and with a
diameter just larger than
the 5/8" seat outside
diameter. I used this as a
tool to press the seat in
until the tool was flush
with the floor of the valve
block, making the seat
stick up 1/16" from the
floor.
I glued the seat in on the pouch side of the block. I then coated the Pouch Well shoulder with
a thin hide glue sizing. This helps insure a good bond when the Pouch Assembly is glued in.
Seal the inside of the block with thick shellac (2-3 lb mix) using a brush to coat all the inside
surfaces and channels. Avoid getting shellac on the Pouch Well shoulder. The sizing will
prevent shellac from bonding to this surface in any even event which is the reason to size this
shoulder first. I use burnt shellac to glue and seal the upper seat and the tracker tube elbow
in place.
While the hole for the bleed cup was still damp with shellac, use a pin punch to tap the bleed
in place. After gluing in the pouch assembly, I used a sharp chisel to cut a V-groove between
the two face holes and the pouch on the pouch side of the valve. This provides air channels
from these holes to the back of the pouch.
I then covered the pouch side of the valve with the fiber-board pouch cover. To make sure
that no glue or glue surface came in contact with the pouch, I glued the board by first pushing
the pouch down against the lower seat and then I rolled hide glue on to the valve block using
a rubber glue roller. I then clamped the fiber-board to the block to dry. This way, no glue
would get on the area of the fiber-board over the pouch.
bobhumes@aol.com
Last Revision 1/31/07
Page 3 Over the years I have used tracker tube
elbows from a supplier whose product
looks like they were made by just bending
and kinking the tube over the corner of a
bench. Although it is true that the channel
inside these tubes are sufficiently large to
work ok, they look like the devil. And they
obviously do not look anything like the
original.
I have always wanted to make my own tubing bender to solve this issue, but procrastination
always won out. With this project, I finally bit the bullet and built the tubing bender shown
here. Email me if you are interested in the details.
Valve Testing and Travel Adjustment
Here is the setup I used to test and adjust the valves. The test pneumatic is made to the
specs of the 105, including the pneumatic movement adjustments and the pallet spring. I
used a dial indicator for setting the valve travel with a rod mounted in the base to mount it
over the valve. I used a quick release clamp to hold the valve during the test/adjust process.
bobhumes@aol.com
Last Revision 1/31/07
Page 4 I build and used the vacuum reservoir I will use for
my 105 as a vacuum source/regulator for testing,
driven by an old PPCo vacuum source. I probably
would not have gone to so much trouble if I did not
want to test various alternative valve seats, valve
leathers and bleed cap combinations. I wanted to
make sure that the valve had good response and
repetition rate so I wanted the valve load and
supply vacuum to match the actual 105 as much as
possible. I set the valve travel to .035". Setting the
travel on the first several valves can be painful with
the frequent removal of the upper seat and turning
of the upper disk. After about 10 valves, you will
get a good feel for a starting point. By the 40
th
valve...you will be an expert! Note that the upper
valve seat does not have to be sealed to set the
travel.
Once the valve travel was set, I sealed the upper valve seat using burnt shellac. After this
set up I was ready to put a coat of finish on the outside of the valves. I used blue masking
tape to cover the pouch cover. I used a punch to make circles of masking tape to cover the
upper seats. The fiber board I used to cover the pouch is very dense and needs no further
sealing. The original valves used a cardboard-like material that was covered with pneumatic
cloth and then shellac to get a good seal. The edges of the cover were chamfered and
sealed to lessen the chance of the board delaminating on the edge. In my case, I covered
the cover with masking tape before chamfering the edges and then chamfered the edge just
before applying a finish. This made a clean finish line and the completed valve has the same
look as the original Wurlitzer valve. Not masking the cover and just spraying it as well would
also be fine. I temporarily put a short section of brass tubing sealed with tape at the end in
the tracker tube hole just far enough to keep the finish from getting in the valve through the
hole. I installed the permanent tracker tube elbow after the shellac dried and sealed it with
burnt shellac. I used an airbru