77 • Flowserve Pump Division ("FPD") for custom, highly-engineered pumps, pre-configured industrial pumps, pump systems, mechanical seals, auxiliary systems and replacement parts and related services; and • Flow Control Division ("FCD") for engineered and industrial valves, control valves, actuators and controls and related services. Our revenue sources are derived from our original equipment manufacturing and our aftermarket sales and services. Our original equipment revenues are generally related to originally designed, manufactured, distributed and installed equipment that can range from pre-configured, short- cycle products to more customized, highly-engineered equipment ("Original Equipment"). Our aftermarket sales and services are derived from sales of replacement equipment, as well as maintenance, advanced diagnostic, repair and retrofitting services ("Aftermarket"). Each of our two business segments generate Original Equipment and Aftermarket revenues. The following table presents our customer revenues disaggregated by revenue source: December 31, 2018 (Amounts in thousands) FPD FCD Total Original Equipment $ 992,162  $ 946,926  $ 1,939,088  Aftermarket 1,628,326  268,285  1,896,611  $ 2,620,488  $ 1,215,211  $ 3,835,699  December 31, 2019 (Amounts in thousands) FPD FCD Total Original Equipment $ 994,719  $ 967,271  $ 1,961,990  Aftermarket 1,709,726  267,981  1,977,707  $ 2,704,445  $ 1,235,252  $ 3,939,697  December 31, 2020 (Amounts in thousands) FPD FCD Total Original Equipment $ 1,091,906  $ 808,585  $ 1,900,491  Aftermarket 1,581,799  245,844  1,827,643  $ 2,673,705  $ 1,054,429  $ 3,728,134 