Taylor-wharton XL-65HP (with dual regulators) Manuel d'utilisateur télécharger pdf (Page 15)

CHECKING CONTAINER PERFORMANCE

Cryogenic containers are two containers, one within the other. The space between the

containers acts as a highly efficient thermal barrier including high technology insulation, a

vacuum, and a vacuum maintenance system. Each serves a very important part in the

useful life of the container. The high technology insulation is very effective in preventing

radiated heat from entering the inner container. The vacuum prevents heat convection or

conduction from reaching the inner container. Unfortunately, the prefect vacuum cannot

be achieved since trace gas molecules being to enter the vacuum space from the mo-

ment of manufacture. The vacuum maintenance systems consists of materials which

gather trace gas molecules from the vacuum space. The maintenance system can per-

form its function for years, but it has a limited capacity. When the vacuum maintenance

system is saturated it can no longer maintain the vacuum integrity of the container. The

change will be very gradual and may go unnoticed for several years. When the vacuum in

the insulation space is no longer effective, the following symptoms may appear:

1. With liquid in the container and pressure building/vaporizer coil not in use, the outer

casing will be much colder than comparative containers.

2. Frost, indicating the liquid level, may be visible on the outer casing of the container.

3. The container may appear to “sweat” if the air surrounding the container is hot and humid.

4. The relief valve will open continuously until the container is empty.

5. The container will hold pressure for several days but will not hold liquid.

NER Testing

If a loss of vacuum integrity is suspected, the container’s Normal Evaporation Rate (NER)

should be checked. The test measures the actual product lost over time so you can

compare the results obtained to the NER value in the SPECIFICATIONS table. A test

period of 48 hours is recommended, after the container is allowed to stabilize, but the

formula given produces a Daily NER over any time period.

1. Fill the container with 125 pounds (57kg) liquid nitrogen.

2. Close the LIQUID valve and the PRESSURE BUILDING valve, leave the VENT valve

open and allow it to remain open during the test.

3. Allow the container to stabilize for 24 hours, then reweigh it. Record the weight, time and

date.

4. Reweigh 48 hours later. The test is more effective if container is not moved during this

period.

The following calculation will provide the actual Normal Evaporation Rate in pounds-per-

day. Daily normal evaporation is simply half the loss over 48 hours.

Daily NER = Weight (Step 3) – Weight (Step 4) x 24

Time between Step 3 and Step 4 in hours

Compare the results of your test to the “as manufactured” NER value in the SPECIFICA-

TIONS section of this manual. A container in service should maintain the NER value of

less than two times the new specification. Any test result greater than two times the

listed value is indicative of a failed, or failing vacuum. If NER is found to be high, contact

Taylor-Wharton Customer Service at (334)443-8680 for disposition.

NOTE:

Fill through the

LIQUID valve with

VENT valve open. The

most Pressure

Building valve must

be closed during the

NER test of P.B.

operation will

increase evaporation

and invalidate test

results.

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 25 26

Commentaires sur ces manuels

Pas de commentaire

Taylor-wharton XL-65HP (with dual regulators) Manuel d'utilisateur Page 15

Commentaires sur ces manuels

Produits connexes et manuels pour Équipement Taylor-wharton XL-65HP (with dual regulators)