Heath Consultants Hi Flow Sampler - Manual (Page 5)

Introduction Hi Flow

Sampler
Instruction 0055-9017 5
1 Introduction
1.1 General Description and Use
WARNING:
The High Flow  Sampler is not to be used in any application that is beyond
its intended purpose or beyond the scope of its specifications. Failure to follow this
warning can result in personal injury or damage to the equipment. For details on
appropriate use, refer to the general description, application, and operation discussions
in this manual.
The Hi Flow  Sampler is a portable, intrinsically safe, battery-powered instrument
designed to determine the rate of gas leakage around various pipe fittings, valve
packings, and compressor seals found in natural gas transmission, storage, processing,
gas gathering, production, offshore, and distribution facilities.
A component’s leak rate is measured by sampling at a high flow rate so as to capture all
the gas leaking from the component along with a certain amount of surrounding air. By
accurately measuring the flow rate of the sampling stream and the natural gas
concentration within that stream, the gas leak rate can be calculated using Equation 1.
The instrument automatically compensates for the different specific gravity values of air
and natural gas, thus assuring accurate flow rate calculations.
Leak = Flow x (Gas
sample
– Gas
background
) x 10 –2 Eq. 1
where:
Leak = rate of gas leakage from source (cfm)
Flow = sample flow rate (cfm)
Gas
sample
= concentration of gas from leak source (%)
Gas
background
= background gas concentration (%)
To ensure that the instrument is capturing all the gas that is escaping from the
component, two measurements are performed at two different flow rates. The first
measurement is taken at the highest possible flow rate, followed by a second
measurement at a flow rate that is approximately 70–80% of the first. If the two
calculated leak rates are within 10% of each other, then it can be assumed that all gas
has been captured during the test.
For those mathematicians who are wondering how both calculations can be the same
with different flow rates, note that the measured CH
4
level at the lower flow rate will be
higher due to less air being drawn in with the sample, thus balancing out the lower flow
rate.
The instrument is packaged inside a backpack, thus leaving the operator’s hands free for
climbing ladders or descending into a confined space.
The instrument is controlled by a handheld Control Unit consisting of an LCD and a 4-key
touch pad, which is attached to the main unit via a 6 foot coiled cord. The Control Unit
comes with two magnets which can be easily attached to a steel pipe, regulator box or
compressor for easy viewing. Alternately, the Control Unit can be used in conjunction
with the neck strap accessory.
The gas sample is drawn into the unit through a flexible 1.5 inch I.D. hose. Various
attachments connected to the end of the sampling hose provide the means of capturing
all the gas that is leaking from the component under test.