Peter Barnes, LLNL
Version 0.1
October 19, 2001

E907 TPC Leak Rate Measurement Procedure

Operation of the E907 TPC in MTest with P10 gas (Ar, 10% methane) is a Risk Class 0 installation. The FNAL ES&H Manual, FESHM, Section 6020.3, governing storage and use of flammable gases, requires that the leak rate of chambers using flammable gas be measured and documented once per year. The specific requirement is:

7. Leaks from experimental devices such as drift chambers shall be measured and documented prior to initial operation (with nonflammable gas, if possible). Leakage above seven liters/hour from any one chamber shall be mitigated. Recheck for leaks after major repairs or modifications, and at least every twelve months. Leakage exceeding 20% of the lower explosive limit at a distance over two inches from an identified "point" leak shall be repaired.

This procedure measures the leak rate of the E907 TPC, and documents the threshold criteria in compliance with requirement 7.

Leak Rate Conversion to Rate of Fall of Pressure

The threshold leak rate, 7 liters/hour, at normal temperature (300 K) and pressure (1 atmosphere), is equivalent to a mass loss of 0.28 moles/hour. In the 2 m3 of the chamber, the instantaneous pressure rate of fall is 709 Pa/h, or 2.85 in H2O /h.

Given an initial gage pressure, P0, the time evolution is

where t is the time constant.

If the initial leak rate is equal to the Requirement 7 threshold value, then the time constant can be determined by differentiating the previous equation and evaluating at t = 0:

With an initial leak rate threshold of 2.85 in H2O /h and an initial gage pressure of 0.5 in H2O, the time constant is 10.5 min. The time history will be:

Time
(min)

Gage Pressure
(in H20)

0

0.50

1

0.45

2

0.41

5

0.31

10

0.19

20

0.07

The leak rate test pressurizes the TPC to 0.5 in H2O, then monitors the pressure for 5 minutes. If the final pressure is greater than 0.31 in H2O, the leak rate is less than the Requirement 7 threshold.

Leak Rate Measurement Procedure

Name

Date

Time

 

 

 

÷ 

Step

Action

 

1.

This measurement is being done with nitrogen gas. (MV-14 is in the nitrogen position.)

 

2.

Stop the flow of nitrogen by closing the flowmeter valves MV-15 and MV-16.

 

3.

If the pressure indication on PI-03 is less than 0.5 in H2O, add more oil to the main bubbler, BUB-02, and start over.

If the pressure indication on PI-03 is greater than 0.5 in H2O, loosen then retighten the quick connect fitting on top of the relief reservoir, RES-01.

 

4.

Slowly open the low rate flowmeter (FI-01) valve, MV-15, allowing gas to pressurize the chamber, until the pressure indication on PI-03 reaches 0.5 in H2O.

 

5.

Record times and pressures on PI-03:

Time

Pressure
(PI-03, in H2O )

Nominal

Actual

Start

 

 

Start + 1 min

 

 

Start + 2 min

 

 

Start + 5 min

 

 

 

6.

Is the final pressure greater than 0.31 in H2O? SYSTEM PASSES

Is the final pressure less than 0.31 in H2O? SYSTEM FAILS and the leak must be found and repaired.