Business segment reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012 Segments	Oct. 31, 2011
Segment reporting
Number of reportable segments			3
Net sales	$ 58,325	$ 71,330	$ 163,314	$ 188,721
Gross profit	11,446	12,432	30,480	31,458
Income (loss) from operations	681	2,232	(1,709)	676
Income (loss) before income taxes	618	2,520	(2,740)	246
Piping Systems [Member]
Segment reporting
Net sales	26,498	35,371	69,147	80,737
Gross profit	6,060	6,222	14,327	13,666
Income (loss) from operations	2,585	3,026	4,183	3,730
Income (loss) before income taxes	3,116	3,709	4,537	4,314
Filtration Products [Member]
Segment reporting
Net sales	20,738	24,000	62,990	74,122
Gross profit	2,616	3,409	8,280	10,258
Income (loss) from operations	(410)	315	(506)	1,341
Income (loss) before income taxes	(410)	315	(506)	1,341
Industrial Process Cooling [Member]
Segment reporting
Net sales	9,199	8,948	27,225	24,334
Gross profit	2,617	2,486	7,586	6,657
Income (loss) from operations	526	517	1,403	1,014
Income (loss) before income taxes	526	517	1,403	1,014
Corporate and Other [Member]
Segment reporting
Net sales	1,890	3,011	3,952	9,528
Gross profit	153	315	287	877
Income (loss) from operations	(2,020)	(1,626)	(6,789)	(5,409)
Income (loss) before income taxes	$ (2,614)	$ (2,021)	$ (8,174)	$ (6,423)