Foreign Materials; Viscosity - Total Control Systems 700-20 Engineering Manual

G) Foreign Materials
Products that are to be measured may have foreign materials present. The inlet side of any
positive displacement meter should be equipped with a strainer. Matching the strainer size or
one size larger, with an appropriate size screen will protect the meter and accessories from
damage in the system. A minimum of 40-mesh screen is recommended for petroleum service.
H) pH
The metal resistance to the effects of high or low
PH is difficult to calculate because of the varying
concentrations and corrosiveness of properties.
This is a generalized rating for pH resistance.
0 1 2
◄——— ACID REACTION ———
I) Viscosity
Viscosity is the property of a fluid that is a measure of its resistance to flow. Among the
earliest to express this quantitatively was Sir Isaac Newton. He reasoned that the viscosity of
a liquid was proportional to its shear stress (or resistance to shear). Liquids that behave in
this manner are referred to as "Newtonian" liquids and are typically by petroleum fluids,
water and similar chemicals.
Other types of fluids are grouped into a general category called "Non-Newtonian" which
includes dilatants, plastic, pseudoplastic and thixotropic. Liquids in this group are
characterized by viscosity that changes with the rate of shear as compared to the Non-
Newtonian fluids where viscosity is basically constant with shear and flow rate. As a
consequence, Newtonian fluids are much easier to predict with regard to their performance
through a flow meter than are the Non-Newtonian liquids.
Many of the more viscous liquids pumped through the 700 series rotary flow meter are
plastic and pseudoplastic and as such are reduced in effective viscosity after being pre-
sheared by the pump. The diagram below shows how viscosity varies as a function of shear
rate on various types of liquids.
pH SCALE
NEUTRAL
3 4 5 6
7
1) Thixotropic Liquids (Plastic and Peudoplastic)
Viscosity decreases as shear rate increases. Typical liquids include
Gels, Latex paints, lotions, Shortening, Mayonnaise, Printers Ink, Hand
cleaner and Yeast.
2) Newtonian Liquids – Viscosity remains unchanged with shear.
3) Dilatants Liquids – Viscosity increases as shear rate increases. Most
liquids in this category are unsuitable with PD flow meters; these
include Clay, Slurries and some confectionary bases.
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Material
Aluminum
Ductile Iron
Ni-Resist
Stainless Steel
8 9 10 11
——— ALKALINE REACTION ——►
pH
5 – 8
5.5 – 11
5.5 – 14
0 – 14
12 13 14