This document is to be used during the vapour washing of the WHT telescope mirrors

Vapour washing of the telescope mirrors

When:

Vapour washing could be necessary if it's really hard to improve the reflectivity parameters with snowcleaning or when there are more massive contamination on the mirror.

Material:

For the vapour washing you need:

• Safety harnesses
• Platform in the tube where you can stand to reach the upper part of the mirror.
• Vaporizing machines (there are two of them) - these are standard carpet cleaner devices, they are producing hot steam
• Pressured air -  you could use the one in in the dome, next to the entrance
• Tape and nylon sheet - the edges of the mirror need to be covered while the vapour washing is in progress

Safety:

• For safety reasons it is preferred to do the vapour washing with two people.
• For vapour washing the WHT there is a safety harness which will keep you in the mirror cell. These can be found in the cupboard reading "Snow cleaning safety equipment".
• You have to secure your harness during the whole process.

Important to know:

• Don't touch the surface of the mirror with the pipe of the pressured air device
• Always secure yourself
• Do the washing with two people - if one is standing on the platform, the other have to support him with handling all the necessary equipment, e.g. the vapour washing machine to the platform

Procedure:

1. Park the telescope in AP3.
2. Open the petals.
3. Install the ladder, connect the orange band on both sides.
4. Install the platform to the right side.
5. Install the nylon sheets to the edges of the telescope, fix it with tapes.
6. Measure reflectivity before the cleaning.
7. Fill the vapour washing machine with deionised water
8. Do the vapour washing for the right side. First do the upper part, standing on the platform, then the lower part standing in the cube. Only wash smaller areas (e.g. in four steps), and immediately after you washed a smaller area use the high pressure air in order to eliminate water drops on the mirror. 
9. Measure reflectivity after the cleaning.
10. Remove the nylon sheets.
11. Repeat the steps from 3-9 to the other side of the telescope.
12. Disassemble the platform
13. Check that there are nothing left in the tube
14. Close the petals.

Procedure for vapour washing using soaped sponge (tested first in December, 2006)

In this case you need sponge, buckets and spray as well.

1. Park the telescope in AP3.
2. Open the petals.
3. Install the ladder, connect the orange band on both sides.
4. Install the platform to the right side.
5. Install the nylon sheets to the edges of the telescope, fix it with tapes.
6. Measure reflectivity before the cleaning.
7. Fill the vapour washing machine with deionised water
8. Spraying with deionised water followed by soap sponging. Note that spraying will put more water on the mirror, be specially careful with drying continuously at the bottom. Clean the sponges carefully first, then prepare a soapy mix, approx. ~3 litres with 1 spoon soap. Important is to soak the sponges completely in the soapy solution so they are absolutely soft. Then carefully tab the mirror with the sponges, no dragging. Press the sponges out before touching the mirror, otherwise you will not be able to catch up with drying.
9. Do the vapour washing for the right side. First do the upper part, standing on the platform, then the lower part standing in the cube. Only wash smaller areas (e.g. in four steps), and immediately after you washed a smaller area use the high pressure air in order to eliminate water drops on the mirror. 
10. Measure reflectivity after the cleaning.
11. Remove the nylon sheets.
12. Repeat the steps from 3-9 to the other side of the telescope.
13. Disassemble the platform
14. Check that there are nothing left in the tube
15. Close the petals.