This system consists of a number of passages in the telescope, fed by holes in various mechanical parts and tied together by tubing, through which air is drawn by a fan outside the base of the telescope. This fan draws air around the mirror, past the azimuth drive tractors, through the fork, out of the electronics boxes, and out of the pump house, then forces it out of the observatory to the north, where presumably it would do the least harm. The fan is designed to be running whenever the oil pumps are running and is activated by the same controls. This picture shows the external parts of the system. For this system to work, a number of parts of the telescope must be sealed up with cover plates and caulking. The base is sealed with plastic insulation under its bottom and between its top and the azimuth drive wheel. The back of the mirror cell is sealed with special covers which must then be caulked. The base skirt is designed to prevent air from moving through the telescope between the base and fork, and there are also two brush seals to retard flow past the azimuth bearing. Various flexible lines leading air from one part of the system to another. First lines on top of the tube take air from the top of the legs of the quadrapod into the tube. Two fans that operate all the time keep the air circulating through the mirror cell and vent it into the observatory. Larger ducts lead air from the electronics boxes into the top of the fork. Other ducts take air passing the drive tractors into the fork. Internal ducts in the fork let the air flow into the base, then out through a door into the airsucker. This sucker has a connection through a semi-flexible duct to the pump room. An 8-inch duct then runs from the sucker to the north wall of the observatory.

1. Ducts on top of the tube: Four ducts lead air passing through legs of the quadrapod (to stabalize their temepreature) into the telescope tube. These are attached to the legs with plastic dogs held by 1/4-20 socket-head cap screws, one of which must be removed to attach the suction line. The other end of each line is attached to a hole in the top of the tube with a cover plate, held on by two 10-32 hex-socket button-head screws.
2. Covers for back of tube: These covers seal the back of the tube (mirror cell) so that air can be sucked from around the mirror. To place the covers, tilt telescope up near its vertical limit; have one technician orient the cover and pass it to a second technician on the telescope. The second technician then should slide the cover between the strut and the mirror cell (pretty easy in this orientation) and attach it with the dogs provided. Finally, seal up the cracks between the covers and the cell as best you can.
3. Tubing on top of the fork: These tubes tie all the outlying parts of the telescope (mirror cell, quadrapod, electronics boxes) into the fork. They are 4-inch flexible mylar ducting with a spiral skeleton of steel. These ducts are attached to couplers to the electronics boxes and directly to the fittings in the covers for the back of the mirror cell with hose clamps. Putting them in place and clamping them down should be straightforward and obvious.
4. Putting the base skirt together: The base skirt consists of four major pieces bolted to the fork and a number of shrouds that fit around the drive tractor. To assemble the skirt, first place the two major pieces going around the drive-tractor attachments and hold them loosly in place with the 1/4-20 button-head screws provided. Each piece is marked with either a "C" or an "R" to indicate which drive tractor it goes over. Next, work the two larger pieces of the skirt into place, possibly using a 1/4-inch guide bolt, dog them into place with the clamps provided, and attach them to the fork with the screws. Tighten the screws holding the shroud to the base, and test the shroud to make sure it doesn't rub the base unduly. If it rubs, you might need to use a hammer or crowbar to make the appropriate modifications. Place the covers over the drive tractors, and secure them with the 10-32 button-head screws provided. Add the "hats" covering the drive motors, and attach these to the fork with the semiflexible ducts.
5. Placement of the Air Sucker: The airsucker is a section of ducting attached to the door sealing the base at one end and with a fan at the other. The door is held on the base with two dogs that press rods into aluminum blocks that then press up against the door. For access to the base, retract the dogs and roll back the airsucker. To close the door, reverse this step.
6. Air filters: Air going into the telescope except through the tube is filtered. There are custom filters at four entry points in the tines of the fork and beneath each azimuth drive tractor. The electronics boxes have rather large standard filters beneath them (which we got at Home Depot). These filters should be washed out or replaced, as appropriate, during the summer shutdown.

The flow of air should be balanced by adding restrictions to the lines with excess flow so as to get an appropriate flow past all the various heat sources. This will be done by trial and error, for instance, by using smoke to watch the flow of air through the system and using a thermometers in the electronics boxes to monitor their temperatures.