OFITE, 11302 Steeplecrest Dr., Houston, TX 77065 USA / Tel: 832-320-7300 / Fax: 713-880-9886 / www.ofite.com
8
Safety
Pressure and Temperature Considerations
Do not use or reconfigure this equipment in a manner not specified in this
manual.
Pressure
There are two reasons for operating at elevated pressures when performing a
filtration analysis.
1. To test fluids at temperatures above the boiling point, the vessel must
be pressurized, which in turn elevates the vapor pressure (boiling
point) so that the fluid remains liquid and does not turn to steam.
2. If testing for drilling applications, pressurization will more approximate
down-hole conditions, enabling the technician to match both bottom
hole temperatures and pressures.
HTHP Filter Presses are pressurized either with Carbon Dioxide or with
Nitrogen gas. The OFITE 175 mL HTHP Filter Press, 170-00 Series, is small
enough to be portable, so it is usually pressurized with small (65 mm length)
Carbon Dioxide (CO
2
) bulbs, which contain 10 cm
3
of CO
2
gas and weigh 8
grams. These bulbs are pressurized to approximately 1,000 PSI and they
contain plenty of carrier gas to run a complete 30 minute filtration test, if run
-
ning the standard API 500 PSI differential test, which is usually 600 PSI on
the top manifold and 100 PSI on the bottom or back pressure.
For temperatures less than 200°F (93°C) a Back Pressure Receiver is not
required as the filtrate will not reach the boiling point. However when operat
-
ing above the boiling point of water, a suitable Back Pressure Receiver is
required, otherwise the test fluid will turn to steam and the test is invalidated.
The standard receiver tube supplied with the 175 mL HTHP Filter Press holds
15 mL of filtrate, so it is very important that the receiver outlet ball valve is
opened after approximately ten seconds of filtrate collection, as a fluid with
poor filtration qualities can easily fill the 15 mL receiver tube almost instan
-
taneously. If this happens the filtrate hopefully will all be ejected from the
safety bleeder valve, but if there is too much fluid volume, the liquid may end
up inside the regulator rendering it useless which will require servicing by a
knowledgeable technician.
Temperature
Normally when one experiences a loss of pressure it is not due to a failure
of the metal alloy in the cell, but rather is a failure of the o-ring or elastomer,
which provides the seal. These o-ring may deform or melt under elevated
temperatures causing a pressurization failure of the cell, which is often sud
-
den and catastrophic. For example, if the valve stem o-ring suddenly fails,
then steam at 400°F and under great pressure may shoot outward horizon
-
tally in one or several directions. A safety shield should always be used when
operating any HTHP Filter Press and especially when one is going to extreme
temperatures and pressures. Above 350°F (176°C) All o-rings must be re
-
placed after each and every test.
