Business segment reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013 Segments	Oct. 31, 2012
Segment reporting
Number of reportable segments			2
Net sales	$ 57,967	$ 47,236	$ 173,460	$ 132,137
Gross profit	16,887	8,676	43,037	22,607
Income (loss) from operations	6,380	185	14,093	(2,837)
Piping Systems [Member]
Segment reporting
Net sales	42,289	26,498	121,825	69,147
Gross profit	14,726	6,060	35,760	14,327
Income (loss) from operations	9,403	2,585	21,276	4,184
Filtration Products [Member]
Segment reporting
Net sales	15,678	20,738	51,635	62,990
Gross profit	2,161	2,616	7,277	8,280
Income (loss) from operations	(486)	(410)	(468)	(505)
Corporate Segment [Member]
Segment reporting
Income (loss) from operations	$ (2,537)	$ (1,990)	$ (6,715)	$ (6,516)