Green’s Dictionary of Slang

1. a questioner, esp. when very boring [pump v. (1)].

1865		Leaves from Diary of Celebrated Burglar 77/1: The turnkey came and asked what was wanted, upon which the ‘pumper’ said in a loud whisper, so that I could hear [...].
1923		J. Manchon Le Slang.

2. anything exhausting, e.g. a running race [one’s pounding heart].

1984

Partridge DSUE (8th edn) 934/1: 1886 in Cassell’s Encyclopoedic Dictionary.

3. (Aus.) the heart [pump n. (1e)].

1930		R. Whitfield ‘Murder in the Ring’ in Black Mask Stories (2010) 358/1: he was getting set to spill something, and his pumper went bad.
1950		(con. 1936–46) K.S. Prichard Winged Seeds (1984) 383: I’m all right [...] The old pumper playin’ up a bit. That’s all.
1962		F. Harvey Strike Command 77: These songs, as the fighter pilots say, ‘really tug at the old pumper’.