Spirax-Sarco, the steam valve and pump maker, saw interim profits tumble 28% as higher impairment charges and challenging trading conditions weighed.Pre-tax profit fell to £30.2m from £41.9m on sales in the half year that rose 5% to £251.6. At constant exchange rates, sales declined 8% against a comparatively strong first half of 2008.Operating costs increased with impairment charges of £7.7m versus £0.6m last year the major drag.The group said it has limited forward visibility of its business levels which month-to-month remain somewhat volatile, although the pace of decline against last year has stabilised in recent months, though markets remain challenging."Subject to continuation of the current favourable exchange rates versus 2008, there is expected to be a further exchange benefit to trading in the second half year, although at current rates of exchange the benefit will be smaller than in the first half year," said the group.It has nearly completed the previously announced headcount reductions. Some of the cost savings benefit began to come through late in the second quarter and it will realise full annualised benefits in the second half year.The board has declared an interim dividend of 10.5p, an increase of 5%.