Business segment reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			12 Months Ended	3 Months Ended	6 Months Ended
	Jul. 31, 2014	Jul. 31, 2013	Jul. 31, 2014 Segments	Jul. 31, 2013	Jul. 31, 2014 Piping Systems [Member]	Jul. 31, 2013 Piping Systems [Member]	Jul. 31, 2014 Piping Systems [Member]	Jul. 31, 2013 Piping Systems [Member]	Jul. 31, 2014 Filtration Products [Member]	Jul. 31, 2013 Filtration Products [Member]	Jul. 31, 2014 Filtration Products [Member]	Jul. 31, 2013 Filtration Products [Member]	Jul. 31, 2014 Corporate Segment [Member]	Jul. 31, 2013 Corporate Segment [Member]	Jul. 31, 2014 Corporate Segment [Member]	Jul. 31, 2013 Corporate Segment [Member]	Jul. 31, 2014 Credit Concentration Risk [Member]	Jan. 31, 2014 Credit Concentration Risk [Member]	Jul. 31, 2013 Sales Revenue, Net [Member]	Jul. 31, 2014 Sales Revenue, Net [Member]
Segment reporting
Number of reportable segments			2
Concentration Risk, Percentage																	28.00%	24.00%	11.00%	14.00%
Net sales	$ 53,370	$ 60,802	$ 112,894	$ 115,493	$ 33,789	$ 43,478	$ 76,143	$ 79,536	$ 19,581	$ 17,324	$ 36,751	$ 35,957
Gross profit	10,545	13,431	26,534	26,150	7,846	10,590	21,304	21,034	2,699	2,841	5,230	5,116
Income from operations	$ 1,795	$ 4,770	$ 7,504	$ 7,303	$ 3,783	$ 6,493	$ 11,800	$ 11,873	$ (30)	$ 501	$ (574)	$ 18	$ (1,958)	$ (2,224)	$ (3,722)	$ (4,588)