Ch. 8 - CHAPTER 8 Temperature and Contamination Control...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
1 CHAPTER 8 Temperature and Contamination Control Fluid Power Circuits and Controls, John S.Cundiff, 2001 INTRODUCTION z Four functions of Hydraulic fluid are z To transmit power z To lubricate z To seal clearances z To provide cooling
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 INTRODUCTION z Hydraulic oil is a lubricant, which transmits power through pressure and flow, but also provides vital cooling and lubrication to moving parts. z For optimum hydraulic component life, the oil viscosity should be maintained in an acceptable range and the contamination level should be minimized. TEMPERATURE CONTROL z Operating temperatures consistently above 160 o F promote chemical reactions that change the properties of the oil. z The effects of high temperature are : z Oxidation of the oil. z Formation of insoluble gums, varnishes and acids. z Deterioration of seals (they harden and leakage begins) z Loss of lubricity z Changes in viscosity
Background image of page 2
3 TEMPERATURE CONTROL z Gums and varnishes clog orifices and cause valves to stick. z Acids attack the metal surface of components causing corrosion. z Most significant effect of high temperature is the reduction in viscosity and subsequent reduction in lubricity. z At some point metal-to-metal contact occurs and damage results. Metal particles from the damaged surface circulate with fluid and erode other surfaces. TEMPERATURE CONTROL z Hydraulic system should be designed to operate at less than 140 o F under worst-case ambient conditions . z Damaged oil will have a darker color and an odor of scorched oil. z Hydraulic energy converts to heat energy when no mechanical work is done at a pressure drop. z Heat is generated when the pump compresses air bubbles in the oil, as pressure is developed by the pump.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 TEMPERATURE CONTROL z Methods for Cooling Hydraulic Oil z Two types of heat exchanger are used to cool hydraulic oil: z Shell-and-tube z Finned tube TEMPERATURE CONTROL z The Shell-and-tube has a series of tubes. z The fluid receiving the heat (typically water) flows around the small tubes.
Background image of page 4
5 TEMPERATURE CONTROL z The finned tube exchanger is used for oil-to-air exchange. z The air may be forced through the exchanger with a fan or may flow naturally. z Oil coolers are not built to withstand pressure; they are mounted in the return line in an off-line loop. TEMPERATURE CONTROL z In Fig 8.3a, t he system flows oil through the heat exchanger. z In Fig 8.3b, system has a separate low-pressure pump to flow oil through the heat exchanger.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
6 TEMPERATURE CONTROL Heat Transfer from Reservoir z Heat is transferred from the reservoir by conduction and convection. z Heat transfer is given by q = u A (T f -T a ) where q = heat transfer (Btu/h) u = overall heat transfer coefficient (Btu/h.ft 2 .
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/22/2011 for the course ABE 5152 taught by Professor Burks during the Fall '08 term at University of Florida.

Page1 / 21

Ch. 8 - CHAPTER 8 Temperature and Contamination Control...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online