Know The Difference Between Pneumatic and Hydraulic Lifts
Pneumatic and hydraulic lifts are two types of lifts that are widely used throughout the industry due to their high load capacities, large extension ranges, and environmental versatility. While several classifications of lifts are available, in the majority of residential, commercial, and industrial applications, the lifting action is typically performed by a pneumatic or hydraulic mechanism. However, mechanical lifts are also available for applications unsuited for pneumatic or hydraulic lifts, such as those requiring limited-range—but precise—movement and quiet operation.
Beyond classification by the lifting mechanism, some of the other design options for lifts include an electric, gas, diesel, or propane power system, portable or stationary, articulating or telescopic, trailer- or truck-mounted, and light or heavy-duty. Based on these various design characteristics, a diverse selection of these lifting devices is available for a wide range of residential, commercial, and industrial applications, including accessibility, maintenance and repair, material handling, personnel moving, transportation, and unloading and loading.
While several varieties of lifts are available, this article focuses on pneumatic and hydraulic lifts, exploring the various designs and types available and explaining their respective functions and mechanisms. Additionally, this article outlines the selection considerations and common applications for each type of lift.
What is (and isn’t) a Lift?
Before going into the details of and differences between the specific classifications of pneumatic and hydraulic lifts, first an understanding of what lifts are—specifically what can and cannot be considered a lift—must be established.
There are several different types of lifting equipment and devices available with similar mechanisms, functions, and names, including lifts. The term “lifts” is an umbrella term referring to the equipment used primarily to raise and lower objects, such as goods, cargo, people, and machinery, for residential, commercial, and industrial applications. Besides lifts, other lifting equipment and devices also include hoists, winches, cranes, elevators, actuators, positioners, manipulators, lifters, and jacks. As described below, each is capable of lifting an object, but their exact mechanism, function, or industrial application may differ from that of lifts, resulting in their classification as a separate category of lifting equipment.
Direction and Application of Lifting Force
Regardless of the type of lift, the force which lifts the object is applied from below, pushing the object upward from the ground. This origin and direction of force distinguish them from other lifting devices, such as hoists, winches, cranes, or elevators, where the lifting force typically originates above the object being lifted, pulling the object upward from the ground. In either case, the application of force allows for vertical—and in some cases, horizontal—displacement of the object, with the difference being whether the force results in a pushing or pulling motion.
Scale and Magnitude of Displacement
Lifts generally operate on the macro-level scale, meaning they are used for lifting applications involving larger objects and displacing objects over more significant distances than other devices, such as actuators and positioners. While these latter devices can produce pushing forces, some of their applications are on the micro-level scale, involving smaller objects and producing relatively small displacement (often measured in microns). Additionally, lifts may incorporate actuating components into the lifting mechanism design to help produce the lifting force, but actuators, in and of themselves, are no lifts. Manipulators—while capable of operating on the macro-level scale—also typically do not move objects over large distances either, only changing the orientation of the object at its original location or moving the object within a small, contained area.
Characteristics of the Lifting Components
Lifters—although nearly identical in the name—are in a category of lifting equipment separate from lifts. In order to lift an object, lifts employ a base component (such as a platform or arms), on which the object rests, and a mechanism, which produces an upward pushing force on the object. Together, these lift components enable the vertical displacement of the object. Lifters can also cause the vertical displacement of an object. However, lifters, such as those utilizing vacuum pressure or lifting magnets, typically must be physically attached to the object for the mechanism to lift it via a pulling motion or, in the case of handheld lifters, require the user provide the force which lifts the object themselves rather than employing a lifting mechanism.
Industrial Delineation of Lifting Equipment
Jacks, such as bottle jacks and drum jacks, can employ similar lifting mechanisms and are used in similar applications to that of lifts. However, despite these similarities, industrial standards typically classify jacks in a category of lifting equipment and devices separate from that of lifts. Therefore, the following article will not cover jacks.
Pneumatic vs. Hydraulic Lifting Mechanisms
Now that a basic understanding of what lifts are and are not has been established, greater description and detail can be given to some of the more specific classifications—i.e., pneumatic and hydraulic lifts.
Lifts employ a variety of actuating components and mechanisms to produce the upward pushing force necessary to lift an object. The three principal actuator types integrated into lift designs are pneumatic, hydraulic, and mechanical, with the first two serving as the most common mechanisms employed.
Pneumatic lifts employ a lifting mechanism which incorporates a hollow cylinder and piston. An external motor or pump moves the piston within the cylinder, increasing the internal air pressure and causing the cylinder to move along the axis of the piston. The cylinder’s motion along the axis creates a linear force which is then used to extend the lift components, raising or lowering the object.
The advantage of employing pneumatic lifts is their collective versatility. Many pneumatic lift models do not require electricity and can be used in a variety of applications, including extreme temperatures and explosion-prone areas. Additionally, pneumatic mechanisms are inexpensive compared to electric and hydraulic ones, are accurate to within in +/-0.1 in., and can generate lifting forces on the order of tens of thousands of pounds force (lbf).
Despite these advantages, pneumatic lifts are limited both by their actuator size and compressor requirements. Throughout the lifting application, operating pressure must be maintained which make pneumatic lifts less-efficient than other types of lifts. This constant pressure requires the constant flow of compressed air, which also increases the overall operating costs. Additionally, pneumatic actuators are typically sized for a specific application, which limits the versatility of a particular lift to the specifications and requirements of the original application.
Hydraulic lifts employ a lifting mechanism similar to that of pneumatic lifts except instead of compressing air, the hydraulic mechanism compresses a liquid (i.e., hydraulic oil) to increase the internal pressure within the cylinder. Like in pneumatic lifts, the increase in internal pressure causes the linear motion of the actuating cylinder which, in turn, raises or lowers the platform and, consequently, the object.
Hydraulic lifting mechanisms are capable of producing up to and greater than 25x the force produced by comparable pneumatic lifting mechanisms. Additionally, they can hold both force and torque constant without the need for continuous fluid flow as with pneumatic mechanisms.
However, unlike pneumatic and electric lifting mechanisms, hydraulic mechanisms have greater environmental impact risks as the components contain hydraulic fluid, which can be detrimental to the environment in the event of a leak. Additionally, hydraulic lifting mechanisms involve several components and parts, leading to a larger space requirement.
Alternative Lifting Mechanism Solutions
For applications unsuitable for pneumatic and hydraulic lifts, mechanical lifts provide an alternative lifting solution. These lifts utilize several different mechanical components depending on the model, including hand cranks, ball screws, lead screws (or power screws), and rack and pinion drives, and can be either hand-operated or powered by an electrical motor. In any of type of mechanical lift, the lifting mechanism functions by translating the radial motion of the components into linear motion which is then exhibited as the extension of the components of the lift and raising or lowering of the intended object.
Electric-powered mechanical lifts offer the greatest control, precision, and accuracy, as well as allow for the lift capabilities to be scalable and repeatable. Compared to pneumatic and hydraulic mechanisms, electric lifting mechanisms produce less noise and present fewer environmental risks due to their lack of fluids. However, electrical lifting mechanisms are typically more expensive and their lifting capabilities—e.g., load capacity, speed, etc.—are limited by the chosen motor, device lifespan, and suitable applications.
Lift Design Characteristics
As outlined above, all lifts are capable of producing an upward pushing force which, when applied to an object, vertically displaces—i.e., raises or “lifts”—it. Beyond these shared qualifications, several options for lift design characteristics are available to suit a wide range of applications, including, as mentioned previously, the type of lifting mechanism employed. Besides this characteristic, the other main design options which an industry professional or procurement agent may consider include:
- Type of power source
Lift Power Source
The power source of a lift typically takes the form of an engine (except for in electric-powered models) and provides the necessary power which runs the lifting mechanism (pneumatic, hydraulic, or mechanical), and, if applicable, the drive system. There are five main types of power sources employed by lifts:
- Dual fuel
Electric-powered lifts are available in both stationary and mobilized models, and, depending on the model, utilizing AC or DC power. Employing a combustion engine-free design powered either by plug-in units or batteries, electric-powered lifts are the only type of lift offering quiet, emission-free operation, which makes them suitable for indoor use. As lift batteries are rechargeable, the long-term fuel costs for battery-powered lifts are typically less than fuel-powered lifts. Additionally, the lift design allows for more compact construction compared to other powered designs, enabling for easier navigation, maneuverability, and storage in enclosed or limited-space applications.
While electric-powered lifts offer some advantages in regards to environmental impact, long-term cost, and mobility concerns, they are limited with respect to platform size, vertical and horizontal extension, and load capacity. Battery-powered lifts also require the integration of a battery charging station, and battery replacements every 2–5 years—depending on use, condition, and maintenance—with prices ranging from $200–$500. While long-term costs of these lifts are typically cheaper than fuel-powered lifts, initial and maintenance costs are relatively high.
Unlike electric-powered lifts, diesel-powered lifts are not emission-free. However, newer diesel engine technology, such as Tier II, III, and IV engines, offers high-performance value, longer operation periods, and lower levels of exhaust emission compared to older diesel-engine models, with some models capable of producing fewer emissions than even dual fuel or gasoline-powered lifts. Typically, these lifts also have larger platform areas, greater vertical and horizontal extension ranges, higher load capacities, and better traction than electric-powered lifts. These advantages make diesel-powered lifts suitable for use outdoors and for rugged-terrain applications, such as construction and industrial job sites.
While newer models produce fewer exhaust emissions, in general, diesel-powered lifts produce more emissions and noise than electric-powered lifts and other engine-powered lifts, such as gas or LP lifts. These limitations make them generally unsuitable for most indoor applications.
Additional limitations surrounding diesel-powered lifts include initial and overall costs. While the cost of the diesel fuel necessary to run a diesel-powered engine is relatively inexpensive—ranging around USD 3–4—the diesel engine itself typically incurs greater investment and maintenance costs than other power sources for lifts. Some diesel-powered models are available at $5,000 premiums compared to gas-powered models, with an estimate in the thousands of dollars regarding the additional cost of oil changes, component replacements, and maintenance and repair over the engine’s lifespan.
Gas-powered lifts, like diesel-powered lifts, employ an internal combustion (IC) engine which produces emissions throughout operation regardless of fuel type—although some fuel types may produce fewer emissions than others during the combustion process. While, compared to electric-powered lifts, these lifts are less environmentally-friendly, they are also capable of employing larger platforms, lifting larger loads, and extending to greater heights and lengths. Several types of gases are used in gas-powered lifts, including gasoline, natural gas, and propane. Depending on the requirements and specifications of the lifting applications, each gas type offers its own advantages and limitations.
Gasoline: Due to the limited availability of refueling stations and the development and the rising popularity of liquid propane (LP) and dual-fuel-powered lifts, gasoline-powered lifts are rarely used. However, if refueling stations are readily available and easily accessible, gasoline-powered lifts can be comparable to other engine-powered lifts. Additionally, the gas-powered design offers greater rearview visibility compared to LP-powered designs and more power, faster travel, and greater platform lift/lower speeds compared to diesel-powered designs.
Natural gas: Similar to gasoline-powered lifts, lifts which employ compressed natural gas (CNG) require ready and easy access to refueling stations to be a cost-effective lifting solution. However, the high cost of the infrastructure necessary for CNG refueling stations—including land, equipment, maintenance, and installation—and the difficulty of obtaining the necessary permits and the gas supply typically make CNG power sources unsuitable for the budgets of most lifting applications.
Given an adequate and accessible CNG refueling infrastructure, compared to other fuels, CNG offers a more environmentally-friendly alternative. Combustion processes which utilize CNG typically produce fewer emissions and, in the event of a gas leak, CNG dissipates into the atmosphere as non-toxic compounds—i.e., water vapor and carbon dioxide. CNG-powered lift designs also do not require the removal of the CNG tank during the refueling process, which allows for less downtime and operator involvement.
Propane: Lifts which employ liquid petroleum gas, also known as liquid propane (LP), offer the lowest initial cost, as LP tanks can be purchased and stored in advance. Replacement of empty tanks is also relatively quick, allowing for less downtime between lifting applications. LP-powered lifts are suitable for both indoor and outdoor applications.
As indicated by the name, dual fuel-powered lifts employ two different types of fuels—gas and diesel. The advantage of employing these types of lifts is their high fuel efficiency compared to other fuel-powered lifts. Additionally, newer dual-fuel-powered models are capable of producing greater horsepower than diesel-only models. However, the cost of the fuel used for dual-fuel lifts (typically liquid propane) is highly variable with costs ranging between USD 2–5 per gallon.
Hybrid-powered lifts employ a combination of the technology from two different types of power sources (typically electric and diesel). Depending on the type of hybrid model—i.e., parallel or series—either or both power sources can power the lift, or the combustion engine acts as a charging generator for the lift’s batteries which power the majority of the lift’s functions, respectively. While series models are less expensive and employ a more compact design than parallel models, parallel models can produce greater power and offer greater flexibility and security due to the power redundancy.
In general, hybrid lift models are capable of operating under extended use and heavy-duty cycles and suitable for both indoor and outdoor applications. The ability to switch to electric-only power, allows for greater operating environment versatility, especially for indoor applications where exhaust emissions must be limited and for outdoor applications where refueling stations are not easily accessible. These advantages come at a cost, however, as hybrid-powered lifts are typically more expensive than a comparable diesel or gas-powered models.
Blog Source: Thomas.net | Understanding Pneumatic and Hydraulic Lifts