1. Field of the Invention
This invention relates to flow regulators and in particular to flow regulators for use in fluid systems having widely and rapidly varying pressure conditions.
2. Description of the Prior Art
In the operation of the lift mechanism of a fork lift truck, fluid systems are utilized which are adapted to rapidly raise and lower the lift means both under relatively heavy and light loads. A problem has arisen in the known fluid controls wherein chattering, overshooting, variable travel rate, and other similar undesirable operation occurs. The problem is aggravated by the relatively wide range of pressure conditions obtaining in such systems in the operation of the lifting mechanism wherein, for example, pressures may vary over the range of approximately 0 to 4000 p.s.i. drop in the regulating system.
In addition, oscillations in the pressure may occur which typically may have a frequency of approximately two oscillations per second, tending to further aggravate the control problem.
One form of flow regulator for use in such applications utilizes a fixed orifice which provides for damping of the oscillations but does not provide such damping at constant speed. Rather, such fixed orifice flow regulators cause a variation in the flow rate with the load thus presenting a serious problem in the accurate control of the load in such fork lift truck applications.
In the fixed orifice flow regulators, sudden pressure changes permit a damped oscillation which may have original substantial excursions causing a chattering effect. Where piston-type flow regulators are utilized, the pressure variation excursions may continue for a substantial period of time presenting a serious chattering problem.