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--obsolete-- 8Pi Dewar Change and Fill Instructions

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Procedures for Christmas shutdown only, and only if 8Pi asks IOps nicely. The diagrams referred to are on the ION in the blue book, usually around the Christmas shutdown.

By 8Pi Folks, Dec. 13, 2006 (Edits in brackets by R. Tanaja, as per A. Andreyev)

 

Purpose and Scope:

This document describes how to change and fill the 180 litre supply dewars on the 8Pi automatic fill system. This procedure must be performed once per day, every 24 hours. Maintenance and operation of the 8Pi autofill system itself are documented separately (http://trshare.triumf.ca/~hackman/ln2.8pi).

This document contains four sections describing groupings of steps in the process - Preparation; Swap Dewars; Fill Dewar; Closeout - and contains Further Information, Contact Information, and some Photographs for guidance at the end.

Preparation:

  1. Read this whole document and familiarize yourself with the location and function of all referenced valves and connections.
  2. This procedure must be performed once a day, starting between 10:00 and 13:30. The procedure takes approximately 30 minutes in total.
  3. During normal operations there are two180 litre dewars at the 8Pi location (figure 1). When you arrive at the 8Pi, you will find one dewar connected to the 8Pi Flex Hose (figure 2). It will have been in service for 24 hours and will not be completely full (figures 3 and 4). This is the used dewar.
    • Note: Dewar valves and ports referred to in subsequent steps are identified in Figure 2.
    • Note: All valves and system parts are labelled with tags.

  4. The other dewar, not yet in service, is the new dewar. Check that it is full; if it is not, fill it first (steps 14 to 29).

  5. Wear appropriate personal protection equipment (PPE). Gloves and eye protection (face shield) are recommended while swapping dewars. Gloves and a face shield are mandatory, and noise protection is recommended, while filling dewars. Tools and PPE are provided at both the 8Pi area and the ISAC fill station.
Swap Dewars:
  1. Close used Dewar Liquid Valve (see Notes under Step 3 in preparation).
  2. Close used Dewar Pressure Building Valve (figure 5).
  3. Open the 8Pi Flex Hose Vent Valve (figure 6) [then close].
  4. Disconnect 8Pi Flex Hose from used dewar liquid port. Two 7/8" box wrenches are provided. Hold the fitting on the hose steady; turn the nut on the dewar (figure 7).
    • The Used Dewar is now ready to bve filled. Fill it after you finish swapping dewars.
  5. Connect 8Pi Flex Hose to New Dewar liquid port.
  6. Close 8Pi Flex Hose Vent Valve.
  7. Open New Dewar Pressure Building Valve (figure 8) [watch pressure gauge and see pressure ?].
  8. Open New Dewar Liquid Valve. YOu may hear a short hiss from a relief valve.

Fill Dewar:

  1. Pull the dewar to the ISAC-I liquid nitrogen filling station (East wall, figure 9).
    • All necessary tools and PPE (see Step 5 in preparation) are at the filling station. Observe any addional precautions or instructions given at the fill station.
  2. Verify that the Dewar Pressure Building Valve is closed (figure 5).
  3. Open the Dewar Vent Valve. [According to A. Andreyev, this step and step 5 should be exchanged in order.]
    • Note: When the dewar is full, cold liquid will discharge from the diffuser in a fanned-out pattern at right angles to the vent port (see figures 10 and 12). Be sure to position the dewar so that once the liquid is flowing you can safely access the valves without reaching or walking through the liquid stream. Check that cold air from the diffuser is not blowing directly onto the filling station valves. Reposition the dewar if necessary.
  4. Connect the Filling Station Flex Hose to the Dewar Liquid Port. [Use the yellow nut on the filling(?) side.]
  5. Close the Filling Station Flex Hose Vent Valve (figure 11). [See note at step 3.]
  6. Open the Dewar Liquid Valve.
  7. Open the Fill Station Main Valve (figure 11).
  8. Move to a place where you will not have to reach or walk through the vapour (and, eventually, liquid) flow in order to access the valves.
  9. Wait patiently (~20 minutes) until liquid is flowing out of the Dewar Vent Port diffuser (figure 12). Intermittent liquid flow is adequate to indicate a full dewar. You will see and hear a change in the flow out of the diffuser when vapour changes to liquid.
    • CAUTION: The liquid nitrogen flowing out of the diffuser can cause frostbite on contact with bare skin. Do not proceed without wearing appropriate PPE (step 5 in preparation).
  10. Close the Dewar Vent Valve.
    • CAUTION: Only perform this step if you are wearing appropriate PPE. Minimize your exposure to the liquid nitrogen flowing out of the diffuser.
  11. Close the Dewar Liquid Valve.
    • CAUTION: For all of steps 11 through 15, the valves, ports, and hoses couls be cold enough to cause frostbite. Do not touch them with bare hands.
  12. Close the Fill Station Main Valve (figure 11).
  13. Open the Flex Hose Vent Valve (figure 11). Wait until there is no audible flow from this valve.
  14. Disconnect the Flex Hose (figure 13) and stow it in the copper pipe (figure 9).
  15. (Open the Pressure Building Valve (figure 8).) [A. Andreyev says this step should be taken out, or you may waste LN2.]
  16. Pull out now-full dewar back to the 8Pi area.

Closeout:

  1. Verify the following:
    • The 8Pi Flex Hose if connected to a full Dewar.
    • The connected Dewar Liquid Valve is Open.
    • The connected Dewar Pressure Building Valve is fully open.
    • The 8Pi Flex Hose Valve is Closed.
    • The 8Pi Flex Hose Pressure is not zero (figure 14).

FURTHER INFORMATION:

The 8Pi detector autofill process occurs daily every eight hours (06:30 to 08:30, 14:30 to 16:30, 22:30 to 00:30). It is best not to swap dewars for an hour after a fill.

The procedure in this document guarantees that there is an adequate quantity of liquid nitrogen in reserve to mitigate a building supply tank failure, no delivery due to weather, etc. This is critical as an unplanned warmup will render one quarter of the detectors unusable.

CONTACTS:

Andrei Andreyev, x6491, 604-224-7601, 604-313-7713, andrei.andreyev@triumf.ca

Greg Hackman (author), x7441, 604-324-9668, 250-752-4730, hackman@triumf.ca

Violeta Toma (reviewer), x7522, violeta@triumf.ca

Gordon Ball, x7334, 604-942-0520, ball@triumf.ca

See also http://trshare.triumf.ca/~hackman/local/cont8pi.htm

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