# Tag Archive: temperature

## SUN cartridges and low temperatures

Recently we got a request from the customer to check the system components to work in a low-temperature environment up to -40°C. Most components in the customer’s system were SUN cartridges.

And I was really surprised by the mess of info on the Sun Hydraulic website about seals that SUN uses in their cartridges.

For example, on the “Seals: Materials of Construction” page you can find the manufacturer’s temperature range: from -22° to 230° F (-30° to 110° C) for Buna N (Nitrile) and -22 to 260° F (-30 to 125°C) for Polyurethane O-rings.

But, if you download Technical Product Information PDF from their library, you can find different temperature range for Buna N: -50°F to 200°F which means -45°C..+93°C and no info about Polyurethane O-rings.

This is why I was confused and had a lot of questions to SUN:

1. Why the different info is provided on SUN website?
2. Why there isn’t a choice for Polyurethane O-rings in seal material when selecting cartridges in the SUN catalog?
3. Why SUN has so high temperatures for the low environment for both Buna N and Polyurethane seals?

Really, all competitors have better low-temperature limits for their cartridges, for example:

– Parker’s Nitrile: from -40°C to +93.3°C
– Danfoss/Comatrol, Buna-N: from -40°C
– Bucher, Buna “N”: from -40°C to +120°C
– Doering, Buna N: from -42.7°C to +93.3°C
– Eaton, Buna N: from -40°C to +120°C
– Hydraforce’ Buna “N”: -40°C to +100°C; polyurethane: -54°C to +107°C.

Because it was critical for my application, I have sent a request directly to SUN to get answers to the questions above and have gotten next response: the correct low work temperature for Buna N is -30°C. Сoncerning the polyurethane seals – this is not a standard option, but any cartridge can be assembled with polyurethane o-rings that provides low temperature rate to -40°C. Not a big difference in the price, but because this is going to be a custom modification the delivery time for cartridges (statement on November 2021) is 15..16 weeks (what actually is not bad for SUN).

## Temperature-Viscosity Chart

The interpolation calculator provided below is used to determine:

• the kinematic viscosity values, depends from temperature, calculated by the formulas specified in ASTM D341 – (‘Standard Practice for Viscosity-Temperature Charts for Liquid Petroleum Products’);
• the Viscosity Index (VI) by the formulas specified in ASTM D2270 (Standard Practice for Calculating Viscosity Index from Kinematic Viscosity at 40 and 100°C 1) or in ISO 2909 (Standard Practice for Calculating Viscosity Index from Kinematic Viscosity at 40 and 100°C 1) or in ГОСТ 25371-2018 (Нефтепродукты. Расчёт индекса вязкости по кинематической вязкости)

#### Annotation.

Any mineral oil is supplied with the specification of kinematic viscosity values at two different temperatures, usually at 40°C and at 100°C (or at 100°F and at 210°F). These data is enough to determine kinematic viscosity at any other values of temperature and as well Viscosity Index.

You can calculate pre-filled values of oil classified by ISO 3448 with grades VG22, VG32, VG46 or VG68 (at viscosity Index = 100) or enter specific values for any other oils.

## Pressure change due to temperature

A change in temperature will cause hydraulic fluid to try to have a corresponding change in volume. If the fluid is trapped in a chamber and is unable to change volume, there will be a change in pressure.

The difference in pressure is based on the bulk modulus (stiffness) of the fluid. A mineral based oil may have a pressure difference of about 11 bar for each 1°C change in temperature (90 psi for each 1°F change in temperature):

## \triangle p=\triangle t\cdot k ##

where k= 90 (imperial units) or k= 11 (metrical units):

## \triangle p\;\lbrack PSI\rbrack\;=\triangle t\;{\lbrack^\circ F}\rbrack\cdot90 ##

what is equal to:

## \triangle p\;\lbrack bar\rbrack\;=\triangle t\;{\lbrack^\circ C}\rbrack\cdot90 ##