HYDRAULICS AND INVERTER Hydraulic lifts represent approximately 40% of the lifts in operation worldwide, the majority with a travel less than 7 floors.In particular there are more than 4.5 million lifts in Europe according to ELA statistics 2009 and with an estimated 1.2 million lifts being the hydraulic type and older than 20 years there are many that could benefit from modernization. Therefore we now see the evolution of the hydraulic pump units to meet the most modern customers’ needs. We will underline during this report the higher efficiency of the latest models that are more environment friendly and that keep the characteristics that the traditional pump units give their success to. Until now, low price, easy installation, project flexibility, quietness, space saving and absence of feedback control awarded success to hydraulic systems. Today customers are looking for the lowest energy consumption and the minimal installed power; consequently the interest in traditional hydraulic drives is “under pressure”, according to a common saying. Usually tenders award hydraulic installations for their well known attention to the safeguard of the users, thanks to the low barycentre of the whole structure and to their easy maintenance procedures. The hydraulicinstallation responds better than all the others to the unforeseeable stresses, such as fires and earthquakes:the kinematics simplicity of hydraulic lifts allows common people living in family houses to easily activate the emergency release, a fact that is very much appreciated by the public bodies and by the local authorities. The counterweight is the fundamental basic elemental difference between electric and hydraulic drives. It allows the electric drives to be more efficient basically from the energy point of view in case of an intensive use of the lift. We will clarify how the most modern technologies have recently permitted the hydraulic pump units to become more convenient in situations which are not exactly a market niche. Hydraulics and inverter till 2009 The technological development on the inverter during the last thirty years has allowed an higher spreading of power electronics in several sectors, the lift drives one included. Motors have consequently gained in efficiency, even economically speaking, through frequency and voltage controllers integrated in the feeding circuit, as inverters are. The motor control through inverter has been firstly experienced in rope lifts due to the programming simplicity of the micro-controller. Basically, in fact, up to 2009 it has not been possible to compensate completely the hydraulic effects, such as elasticity, viscosity, pressure drop, in the hydraulic lifts, through programming, especially during the downward travel. The first hydraulic pump units with inverter were shown to the market during later half of the 80s, as some producers underline proudly: unfortunately their inverter only partially worked during the upward travel of the car. These systems are still sold and in this case the valve traditionally assembled on the pump units still regulates the downward travel, with a clear cost increase, together with the complicated operation of installing in the shaft a control system of the car position (encoder).
Posted on: Sat, 13 Jul 2013 07:49:30 +0000
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