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   Tropari - Water Damage
                   
 

Preventing Instrumet Water Damage

 
                   
  General
 
 

A water soaked instrument that has been allowed to sit on the shelf, or is a few weeks or more in transit for repairs, is a sad mess inside. The electro-chemical reactions between the metals in the timing and locking mechanism have usually ruined most of the internal parts. Salt or acid-rich water just increases the extent of the damage.

 
         
  Prevention
 
 

Damaged containers are usually the major cause of water soaked instruments. Nearly 25% of container damage is caused by pipe wrenches which have "missed" the solid hexagon cap of the container and bridged the metal to metal join during closure or opening. Only use the custom Pajari Container wrenches provided.

The water proof joints and threads on our containers are precision machined to give an exacting fit, so that tightening up with two 16" (40 cm) wrench handles will secure the seal faces even when the container is subject to shock. Our new containers (3C) have an internal O-Ring to give an additional level of waterproof sealing.

When the thread size on the container cap is increased by using Teflon tape, viscous or dried sealants, the threaded end of the container body is expanded producing a slight funnel shape resulting in a loose fitting cap. When this occurs, all of the precision fit surfaces no longer match and the seals are no longer effective. Inevitably the container will leak because at some time an insufficient sealant will be used - or the cap will become so loose that the strength of the sealant will no longer be sufficient to hold back the water pressure.

Do not use Teflon tape or other sealants.

 
                   
  Container Care
 
 

Keep the threads, O-Rings. shock absorbers and the inside of the container clean. Keep the container threaded together when not in use so that the threads and seals cannot be damaged accidentally. Use a light coating of oil on the threads to diminish wear. Send in your container periodically for inspection (and repairs if required.)

 
     
  Condensation
 
 

When the instrument is colder than the dew point of the surrounding air, condensation of moisture from the air will occur. This happens in all environments from the tropics to the poles - on the surface and underground. If the instrument inside the container is brought to the same temperature as the air before it is removed from the container, no condensation will occur. To prevent condensation on the instrument, any method that warms the instrument inside the container to the air or a higher temperature will work. A few examples are given below:

  • when the container is retrieved from the hole, let it warm up in the sun (5 min.) before opening it, or

  • heat the container with a propane torch until it is quite warm to the hand (don't worry about damaging the instrument - as long as the container never gets hotter than what your hand can bear, the instrument inside is perfectly safe) and leave for 3-4 minutes for the heat to be transferred to the instrument inside, or

  • bring a plastic thermos jug nearly filled with hot water and dump the container into the water for 3-4 minutes before removing the instrument.

These are a few examples of heat sources that can be used to prevent condensation - others may be available at your drill site. Prevention of condensation is the easiest and wisest procedure. If you do have a damp instrument, dry it as soon as possible.

  • DO NOT store the instrument in a surveying container - containers that have been used will be moist (especially the shock absorbers).

  • DO NOT store a moist instrument by placing it in a box or transit case.

  • DO NOT leave instruments in moist environments for any longer than a few days. (e.g. underground in mines and drill shacks in the wet tropics.)

 
       
  Water Damage - Damage Minimization
 
 

Do store dry instruments carefully - A dry instrument inside its dry box and placed in a sealed plastic bag will be ready to use at any time irrespective of the environment.

When Prevention Fails - Minimize the Damage - Here we are concerned with a range of prevention breakdowns from a water-filled container and instrument to short-term exposure to condensation or moisture.

What to do with a dripping wet Instrument?

First - get the water out by immersing the instrument in a container of methyl alcohol, methyl hydrate, acetone or any liquid that will combine with water. Remove the instrument and shake gently (to mix the water and solvent inside) and let drain. Repeat if necessary.

Second - coat the internal surfaces by immersing the instrument in oil - the thinner the oil, the more penetrative it will be. If you use a plastic bag as a container and seal the top you can periodically shake the bag so that the oil will coat the inside surfaces. Diesel oil, machine oil - or any oil available. Let the oil drain before sending the instrument (wrapped in plastic) for servicing. There is no need for extreme haste as a few hours delay in these procedures is not critical except in the most acid waters - but the sooner the better. If you can't do both steps - do the one that is possible. Some rust and lubrication fluids (like WD-40) serve both purposes.

Condensation and Moisture Control - if condensation has appeared on the instrument, or in more severe cases inside the visible compass compartment, the water can be removed by warming the instrument to a temperature that is warm to hot-to-touch, but not beyond the temperature where the instrument is painful to handle (maximum 105° C). When condensation has disappeared, the instrument is safe from the possible harmful effects of condensation.

Moisture - a less severe case of condensation can also be eliminated by warming the instrument.

  • in temperate climates, leaving the instrument box open exposing the instrument to a warm, dry room overnight is sufficient to remove internal moisture.

In wet climates, condensation and moisture are a constant problem with all equipment, especially under long term field conditions. By establishing a daily routine procedure (e.g. using a lidded box with one or more light bulbs into which all surveying instruments are placed after the days work) may provide you with a dry instrument the following morning. Try to establish a procedure for your surveying conditions - the drier the better.


Condensed from "The Selective Surveyor" Vol. 2, No. 2, November 1991 (revised April 1995)

 

 
  GIT2-10-12-2004  
       

 

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