{"id":1459,"date":"2026-06-10T11:34:02","date_gmt":"2026-06-10T09:34:02","guid":{"rendered":"https:\/\/www.tfsoleodinamica.it\/case-study\/basic-concepts-of-hydraulics\/"},"modified":"2026-10-07T12:58:16","modified_gmt":"2026-10-07T10:58:16","slug":"basic-concepts-of-hydraulics","status":"publish","type":"case-study","link":"https:\/\/www.tfsoleodinamica.it\/en\/case-study\/basic-concepts-of-hydraulics\/","title":{"rendered":"Hydraulics: what it is and how it works \u2013 basic concepts guide"},"content":{"rendered":"\n<article class=\"tfs-cs\">\n  <header class=\"tfs-cs-hero\">\n    <div class=\"tfs-cs-eyebrow\">\u2699 Guide \u00b7 Hydraulic technology<\/div>\n    <h1>Hydraulics: what it is and how it works<br><span>principles, components and applications, explained by the workshop<\/span><\/h1>\n    <div class=\"tfs-cs-meta\"><span><strong>Topic<\/strong> Fundamentals<\/span><span><strong>Fields<\/strong> Industry \u00b7 Marine \u00b7 Earthmoving \u00b7 Energy<\/span><span><strong>Edited by<\/strong> TFS technical team<\/span><\/div>\n  <\/header>\n  <figure class=\"tfs-cs-cover\"><img decoding=\"async\" src=\"https:\/\/www.tfsoleodinamica.it\/wp-content\/uploads\/2026\/05\/motori-oleodinamici-hero-618-1024x576.jpg\" alt=\"Hydraulics: what it is and how a hydraulic system works\"><\/figure>\n  <div class=\"tfs-cs-body\">\n    <p class=\"tfs-cs-intro\"><strong>Hydraulics<\/strong>, or more precisely oil hydraulics, is the technology that transmits and controls power through <strong>pressurised oil<\/strong>. A pump turns the mechanical energy of a motor into hydraulic energy; valves and pipes carry it where it is needed; a cylinder or a hydraulic motor converts it back into force or torque. It is the technology that lifts an excavator arm, closes a press rated at hundreds of tonnes, steers a ship and opens the gate of a dam.<\/p>\n\n    <h2>The principle: why a liquid transmits force<\/h2>\n    <p>Everything rests on <strong>Pascal\u2019s law<\/strong>: pressure applied to a confined fluid is transmitted equally to every point of the fluid. Unlike air, oil is practically incompressible, so every bar of pressure generated by the pump reaches the actuator without being \u201cabsorbed\u201d by the fluid.<\/p>\n    <p>The resulting force is pressure multiplied by the area it acts on. A concrete example: a cylinder with a 100 mm piston has an area of about 78.5 cm\u00b2. Fed at 200 bar, it pushes with a force of about 157,000 newtons, that is <strong>roughly 16 tonnes<\/strong>, from a component you can hold in one hand. This force density is what makes hydraulics irreplaceable wherever high loads meet tight spaces.<\/p>\n\n    <h2>Hydraulics and pneumatics: the differences<\/h2>\n    <ul class=\"tfs-cs-list\">\n      <li><strong>Hydraulics<\/strong>: in industrial practice the word almost always means oil hydraulics, with typical working pressures between 100 and 350 bar on industrial systems and mobile machinery. The oil transmits power and, at the same time, lubricates and cools the components.<\/li>\n      <li><strong>Pneumatics<\/strong>: uses compressed air, normally between 6 and 10 bar. Air is compressible: pneumatics is clean, fast and inexpensive, but develops much lower forces and positions with less stiffness. Where force, precision under load or holding a position are needed, hydraulics takes over.<\/li>\n    <\/ul>\n\n    <h2>How a hydraulic system works<\/h2>\n    <p>Every <strong>hydraulic system<\/strong> performs a double energy conversion: from mechanical to hydraulic, and back from hydraulic to mechanical. The path is always the same:<\/p>\n    <ul class=\"tfs-cs-list\">\n      <li><strong>Prime mover<\/strong>: an electric motor or a combustion engine drives the pump<\/li>\n      <li><strong>Pump<\/strong>: draws oil from the tank and delivers it into the circuit, generating flow<\/li>\n      <li><strong>Valves<\/strong>: control pressure, flow and direction<\/li>\n      <li><strong>Actuators<\/strong>: hydraulic cylinders and motors, which turn the energy of the fluid into force or torque<\/li>\n      <li><strong>Return<\/strong>: the oil flows back to the tank through the filters and, where fitted, the heat exchanger<\/li>\n    <\/ul>\n    <p>One point we often have to explain in the workshop: <strong>the pump generates flow, not pressure<\/strong>. Pressure arises from the resistance the oil meets, that is from the load to be moved. A pump discharging freely to tank works at almost zero pressure; the same pump pushing a loaded cylinder rises up to the setting of the relief valve. This is why, when a system \u201chas no pressure\u201d, the pump is only one of the suspects: the cause is often a valve discharging to tank or an internal leak.<\/p>\n\n    <h2>The components of a hydraulic circuit<\/h2>\n    <ul class=\"tfs-cs-list\">\n      <li><strong>Pumps<\/strong>: <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/catalog\/gear-pumps\/\">gear pumps<\/a>, vane pumps or <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/catalog\/piston-pumps\/\">piston pumps<\/a> (axial and radial); fixed or variable displacement, when the flow must follow the demand of the load<\/li>\n      <li><strong>Linear actuators<\/strong>: <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/catalog\/cylinders-and-actuators\/\">hydraulic cylinders<\/a>, single or double acting<\/li>\n      <li><strong>Rotary actuators<\/strong>: <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/catalog\/hydraulic-motors\/\">hydraulic motors<\/a>, gear, orbital, axial piston and radial piston types, up to the low-speed high-torque motors used on winches and mills<\/li>\n      <li><strong>Valves<\/strong>: pressure valves (relief, reducing, sequence), flow valves, <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/catalog\/valves-and-distributors\/\">directional valves<\/a>, up to <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/catalog\/servo-valves-and-proportional-valves\/\">proportional valves and servo valves<\/a> for precise electronic control<\/li>\n      <li><strong>Tank<\/strong>: holds the oil, lets it settle, separates the air and helps dissipate heat<\/li>\n      <li><strong>Filters, accumulators and heat exchangers<\/strong>: keep the oil clean, store energy and absorb pressure peaks, control temperature (<a href=\"https:\/\/www.tfsoleodinamica.it\/en\/catalog\/filtration-accumulators-fluid-conditioning\/\">filtration and fluid conditioning<\/a>)<\/li>\n      <li><strong>Pipes, fittings and instruments<\/strong>: connect the components and measure pressure, temperature and level<\/li>\n    <\/ul>\n    <p>When motor, pump, tank, filters and main valves are assembled into a single unit, it is called a <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/case-study\/design-of-hydraulic-control-units\/\">hydraulic power unit<\/a>: the heart of the system, while the actuators sit on the machine.<\/p>\n\n    <h2>The hydraulic schematic<\/h2>\n    <p>Hydraulic systems are designed and documented with a <strong>hydraulic schematic<\/strong> drawn with the standard graphic symbols of <strong>ISO 1219<\/strong>: each component has its own symbol, and anyone who reads the symbols understands how the circuit works without seeing the machine.<\/p>\n    <p>The simplest circuit, the first one everybody studies, includes a pump drawing from the tank, a relief valve protecting the circuit from overload, a three-position directional valve that extends, retracts and stops a double-acting cylinder, and a filter on the return line. Real systems add speed control, control of suspended loads, several simultaneous users and, more and more often, electronic control. The schematic, however, remains the first document to ask for before working on a system: without it, every diagnosis takes longer.<\/p>\n\n    <h2>The fluid: hydraulic oil<\/h2>\n    <p>Oil is not just the medium that transmits power. It lubricates moving surfaces, carries heat away, protects against corrosion and seals parts mated with clearances of a few microns. Its selection starts from <strong>viscosity<\/strong>, expressed by the ISO VG grade (32, 46 and 68 are the most common), according to operating temperatures and the components installed.<\/p>\n    <p>Its condition decides the life of the system. <strong>Contamination<\/strong> by particles, water and air is the most frequent cause of wear and failure in hydraulic components: this is why oil cleanliness is measured with a coded class (ISO 4406) and maintained with <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/case-study\/hydraulic-oil-filtration\/\">adequate filtration<\/a>, not judged by eye.<\/p>\n\n    <h2>Where hydraulics is used: applications<\/h2>\n    <ul class=\"tfs-cs-list\">\n      <li><strong>Industry<\/strong>: presses, machine tools, moulding and rolling plants, steel lines<\/li>\n      <li><strong>Earthmoving and agriculture<\/strong>: excavators, loaders, cranes, tractors and implements<\/li>\n      <li><strong>Marine and offshore<\/strong>: winches, deck cranes, steering gear, hatches, stabilisers<\/li>\n      <li><strong>Energy<\/strong>: oil &amp; gas, turbine governing and gate operation in hydroelectric plants<\/li>\n      <li><strong>Railway<\/strong>: suspensions and on-board actuators, track maintenance machines<\/li>\n    <\/ul>\n    <p>For each of these fields we describe components and selection criteria in our <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/sectors\/\">industry sector pages<\/a>.<\/p>\n\n    <h2>Advantages and limits of hydraulics<\/h2>\n    <p><strong>The advantages<\/strong> are the reason hydraulics holds its ground in an increasingly electric world: very high forces and torques from compact components, stepless control of speed and force, built-in overload protection thanks to the relief valve, the ability to hold a load in position, and power transmission far from the motor through simple pipes.<\/p>\n    <p><strong>The limits<\/strong> must be known in order to design and maintain systems well: part of the energy turns into heat that has to be removed, components are sensitive to contamination, seals can leak, some pumps are noisy. Today many of these limits are reduced by variable displacement pumps, variable speed drives and electronic control, which make the system work only when and as much as needed.<\/p>\n\n    <h2>Why a hydraulic system fails<\/h2>\n    <p>In the workshop we see the same causes every day, almost always combined:<\/p>\n    <ul class=\"tfs-cs-list\">\n      <li><strong>Contamination<\/strong>: particles that score pistons, plates and valve spools<\/li>\n      <li><strong>Overheating<\/strong>: oil running above its design temperature loses viscosity, degrades and leaves surfaces without a lubricating film<\/li>\n      <li><strong>Cavitation and aeration<\/strong>: vapour or air bubbles that collapse and erode surfaces; we describe them in detail on our <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/services\/hagglunds-motor-repair\/\">H\u00e4gglunds motor repair<\/a> page<\/li>\n      <li><strong>Wear and settings<\/strong>: clearances that open up with operating hours, valves set wrongly or tampered with<\/li>\n    <\/ul>\n    <p>Identifying the cause is decisive: replacing a pump without removing what damaged it means seeing it back in the workshop within a few months. This is why every component we repair is dismantled, measured and then <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/services\/test-bench\/\">tested on a test bench<\/a> with measured values, not estimates.<\/p>\n\n    <h2>Key quantities<\/h2>\n    <ul class=\"tfs-cs-list\">\n      <li><strong>Pressure<\/strong> (bar): determines the available force or torque<\/li>\n      <li><strong>Flow<\/strong> (l\/min): determines the speed of the cylinder or motor<\/li>\n      <li><strong>Displacement<\/strong> (cm\u00b3\/rev): the volume of oil moved by a pump or motor at each revolution<\/li>\n      <li><strong>Hydraulic power<\/strong>: in kW it equals pressure in bar times flow in l\/min, divided by 600; 200 bar and 60 l\/min correspond to 20 kW<\/li>\n      <li><strong>Viscosity<\/strong>: the oil\u2019s resistance to flow, which changes with temperature<\/li>\n      <li><strong>Internal leakage<\/strong>: oil passing internally between mating parts; it grows with wear and lowers efficiency<\/li>\n    <\/ul>\n\n    <h2>Hydraulics as TFS sees it<\/h2>\n    <p>Since 1997 TFS has worked on industrial hydraulics from the point of view of those who repair, design and maintain systems: <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/services\/pump-and-motor-repair\/\">repair and overhaul of pumps and motors<\/a> of every brand, <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/services\/design-of-hydraulic-systems\/\">design of hydraulic systems<\/a> and power units, scheduled maintenance and testing on test benches up to 470 bar and 600 l\/min. For more specific questions we have collected the most frequent answers in our <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/faq\/\">FAQ<\/a>.<\/p>\n\n    <h2>TFS technologies and services involved<\/h2>\n    <ul class=\"tfs-cs-links\"><li><a href=\"https:\/\/www.tfsoleodinamica.it\/en\/catalog\/\">Hydraulic components catalogue<\/a><\/li><li><a href=\"https:\/\/www.tfsoleodinamica.it\/en\/services\/pump-and-motor-repair\/\">Pump and motor repair<\/a><\/li><li><a href=\"https:\/\/www.tfsoleodinamica.it\/en\/services\/design-of-hydraulic-systems\/\">Hydraulic system design<\/a><\/li><li><a href=\"https:\/\/www.tfsoleodinamica.it\/en\/services\/scheduled-maintenance\/\">Scheduled maintenance<\/a><\/li><li><a href=\"https:\/\/www.tfsoleodinamica.it\/en\/services\/test-bench\/\">Test bench<\/a><\/li><\/ul>\n  <\/div>\n  <div class=\"tfs-cs-cta\">\n    <h3>Do you have a hydraulic system to repair or design?<\/h3>\n    <p>Tell us about your needs: the TFS technical team is here to help.<\/p>\n    <a href=\"https:\/\/www.tfsoleodinamica.it\/en\/contact-us\/\" class=\"tfs-cs-cta-btn\">Contact us \u2192<\/a>\n  <\/div>\n<\/article>\n\n","protected":false},"excerpt":{"rendered":"<p>\u2699 Guide \u00b7 Hydraulic technology Hydraulics: what it is and how it worksprinciples, components and applications, explained by the workshop Topic FundamentalsFields Industry \u00b7 Marine \u00b7 Earthmoving \u00b7 EnergyEdited by TFS technical team Hydraulics, or more precisely oil hydraulics, is the technology that transmits and controls power through pressurised oil. A pump turns the mechanical&#8230;<\/p>\n","protected":false},"featured_media":905,"menu_order":0,"template":"","meta":{"_acf_changed":false,"_kad_blocks_custom_css":"","_kad_blocks_head_custom_js":"","_kad_blocks_body_custom_js":"","_kad_blocks_footer_custom_js":"","_kad_post_transparent":"","_kad_post_title":"hide","_kad_post_layout":"fullwidth","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_kad_post_classname":""},"class_list":["post-1459","case-study","type-case-study","status-publish","has-post-thumbnail","hentry"],"acf":[],"taxonomy_info":[],"featured_image_src_large":["https:\/\/www.tfsoleodinamica.it\/wp-content\/uploads\/2026\/05\/motori-oleodinamici-hero-618-1024x576.jpg",1024,576,true],"author_info":[],"comment_info":"","_links":{"self":[{"href":"https:\/\/www.tfsoleodinamica.it\/en\/wp-json\/wp\/v2\/case-study\/1459","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.tfsoleodinamica.it\/en\/wp-json\/wp\/v2\/case-study"}],"about":[{"href":"https:\/\/www.tfsoleodinamica.it\/en\/wp-json\/wp\/v2\/types\/case-study"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.tfsoleodinamica.it\/en\/wp-json\/wp\/v2\/media\/905"}],"wp:attachment":[{"href":"https:\/\/www.tfsoleodinamica.it\/en\/wp-json\/wp\/v2\/media?parent=1459"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}