Pumping the dewar

We use the services and equipment of KPNO to pump the vacuum on our dewar. Our contact is Bill Binkert at KPNO. Here is the procedure:

1. Plan the dewar pumping in advance! The KPNO vacuum pump and personnel will have to be available. While the pump is attached to the telescope, it can't be moved, so telescope users will have to be informed of this.
2. KPNO is keeping an adaptor hose for us which makes the connection between the large gauge opening on their vacuum pump and the valve on the side of our dewar. Remind them that they will need this. It should be kept with their vacuum pump supplies.
3. Check with EOST for new (and perhaps changing) procedures involving safe operation of the observatory. What follows is a sketch of what might be done...
4. Make sure the telescope is stowed at its zenith position.
5. Insert the steel staybar to prevent the telescope from moving. This is a heavy metal brace that runs between the concrete floor next to the control room and the counterweight on the RA axis of the telescope.
6. Switch the manual override panel to manual mode. Turn the keyswitch clockwise to put it in manual mode. The yellow light next to the switch should turn on.
7. Release the emergency stop(s). There are two, one of which might be on. One is to the right, on the outside of the control room door. Simply twist this button clockwise to release it. The light should then go out. The other is on the control panel on the control room desk. Pull this one out to release it.
8. Raise the platform to the position just short of the camera (this is probably at its topmost position).
9. Now push in the emergency stop button. This should prevent the telescope from moving.
10. Place the KPNO vacuum pump on the platform next to the dewar in a place where it is easy to attach. KPNO people can help attach it. You'll need a screwdriver to cinch the end of the rubber hose down on the entrance to the dewar.
11. KPNO people will operate their own dewar, unless you arrange otherwise. The first thing they should do is to evacuate parts of the hose leading up to the dewar, starting with the chambers closest to the pump. This takes a minute or so.
12. When the hose is close to a vacuum, slowly unscrew the valve leading into the dewar (the black know on the side of the dewar). If the dewar isn't terribly flat and the hose is sealed well, there shouldn't be sound of rushing air. If all seems well, continue opening the valve until it is wide open. The valve should not be opened quickly at first in case there is air in the dewar... thin insulation inside the dewar could be blown out of place.
13. Probably (based on just a few experiences), the turbo pump will fully evacuate the dewar in a few hours. If the dewar was completely flat, it might take longer. If the dewar had been very flat for an extended period of time and you believe it might have contaminants inside, you'll probably have to warm it up ( 1 day) before pumping to make sure the contaminants are liquid or gaseous so that they can be pumped out. In that case, once the pump has been on the dewar for a while, turn the Cryotiger back on to cool the dewar. The last bit of pumping should always be done while the dewar is cold.
14. When done, tighten the valve leading into the dewar. Turn off the vacuum pump. When the vacuum pump has spun down sufficiently, unhook the hose.
15. Once again, to lower the floor, the emergency stop(s) must be released. To observe again, you'll want to lower the floor all of the way.

Figure 8.1: A KPNO turbo vacuum pump attached to the dewar. The floor has been moved up high close to the camera with the telescope at zenith. The red hose leading into the dewar is an adaptor that KPNO configured for the RCT.