Business segment reporting (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2015 USD ($)	Oct. 31, 2014 USD ($)	Oct. 31, 2015 USD ($) Segments	Oct. 31, 2014 USD ($) Rate	Jan. 31, 2015
Segment reporting
Number of reportable segments | Segments			2
Net sales	$ 66,316	$ 43,819	$ 144,051	$ 156,713
Gross profit	16,971	6,721	26,672	33,255
Income (loss) from operations	7,360	(1,236)	$ 85	6,268
Piping Systems [Member]
Segment reporting
Segment Reporting Information, Description of Products and Services			Piping Systems, which engineers, designs, manufactures and sells specialty piping, leak detection and location systems
Net sales	46,950	26,540	$ 92,374	102,683
Gross profit	14,315	4,609	19,796	25,913
Income (loss) from operations	9,721	1,096	$ 7,470	12,896
Filtration Products [Member]
Segment reporting
Segment Reporting Information, Description of Products and Services			Filtration Products, which manufactures custom-designed industrial filtration products to remove particulates from air and other gas streams
Net sales	19,366	17,279	$ 51,677	54,030
Gross profit	2,656	2,112	6,876	7,342
Income (loss) from operations	(162)	(726)	(1,337)	(1,300)
Corporate Segment [Member]
Segment reporting
Income (loss) from operations	$ (2,199)	$ (1,606)	$ (6,048)	$ (5,328)
Credit Concentration Risk [Member]
Segment reporting
Concentration Risk, Percentage			17.00%		31.00%
Sales Revenue, Net [Member]
Segment reporting
Concentration Risk, Percentage | Rate				12.60%