A pressure regulator for use in regulating the outlet pressure of a pump for use in an engine comprises a piston member which is moveable with respect to an outlet opening under the influence of fluid pressure acting on the piston member to control the degree by which the outlet opening is obscured. The cloud tracking system for photovoltaic power plant can include plurality of cloud shadow sensors positioned on the perimeter of the photovoltaic power plant. The mounting openings may be configured for a flexible securing material, e. said frame strips consists of at least two individual elements which are oriented perpendicularly to the direction of flow, engage with each other in a positively locking manner, and or can be interconnected.