Downhole drilling tool

A valve component for use in a drill string, the valve component comprising:

• a flow head comprising a plurality of ports permitting fluid communication therethrough, the plurality of ports including ports of different sizes;
• a flow restrictor comprising a plurality of ports permitting fluid communication therethrough, the plurality of ports including ports of different sizes;
• the plurality of ports of the flow head being arranged such that eccentric rotation of the flow head with respect to the flow restrictor causes one or more of the plurality of ports of the flow head to enter into and out of alignment with one or more of the plurality of ports of the flow restrictor, such that fluid flow through the ports of the flow head and the flow restrictor is varied in an irregular pattern, the irregular pattern comprising a pattern in which an orientation of the flow head at a defined position in a cycle of the rotor is different between consecutive cycles of the rotor.

A method of varying drilling fluid pressure in a drill string, the method comprising:

• varying flow of the drilling fluid in the drilling string above a drilling tool of the drilling string in an irregular pattern, the irregular pattern being determined by flow of the drilling fluid through a flow head and a flow restrictor, the flow head being driven by a rotor in eccentric rotation with respect to the flow restrictor, each of the flow head and the flow restrictor comprising a plurality of ports, the plurality of ports in the flow head comprising different sizes and the plurality of ports in the flow restrictor comprising different sizes, wherein the flow of the drilling fluid is determined by alignment of any of the plurality of ports of the flow head with any of the plurality of ports of the flow restrictor, the irregular pattern comprising a pattern in which an orientation of the flow head at a defined position in a cycle of the rotor is different between consecutive cycles of the rotor.