Dividend investing is a tried-and-true strategy for generating strong, steady returns in economies both good and bad. But as corporate America's slew of dividend cuts and suspensions over the past few years has demonstrated, it's not enough simply to buy a high yield. You also need to make sure those payouts are sustainable.

Let's examine how Air Products & Chemicals (NYSE: APD) stacks up. In this series, we consider four critical factors investors should examine in every dividend stock. We'll then tie it all together to look at whether Air Products is a dividend dynamo or a disaster in the making.

1. Yield
First and foremost, dividend investors like a large forward yield. But if a yield gets too high, it may reflect investors' doubts about the payout's sustainability. If investors had confidence in the stock, they'd be buying it, driving up the share price and shrinking the yield.

Air Products yields a moderate 2.6%, bit higher than the S&P 500's 2.1%.

2. Payout ratio
The payout ratio might be the most important metric for judging dividend sustainability. It compares the amount of money a company paid out in dividends last year to the earnings it generated. A ratio that's too high -- say, greater than 80% of earnings -- indicates that the company may be stretching to make payouts it can't afford, even when its dividend yield doesn't seem particularly high.

Air Products has a modest payout ratio of just 37%.

3. Balance sheet
The best dividend payers have the financial fortitude to fund growth and respond to whatever the economy and competitors throw at them. The interest coverage ratio indicates whether a company is having trouble meeting its interest payments -- any ratio less than 5 is a warning sign. Meanwhile, the debt-to-equity ratio is a good measure of a company's total debt burden.

Air Products has a debt-to-equity ratio of 77% and interest coverage of 14 times.

 4. Growth
A large dividend is nice; a large growing dividend is even better. To support a growing dividend, we also want to see earnings growth.

Over the past five years, Air Products' earnings per share have shrunk at an annualized rate of 12%, while its dividend has grown at an 11% rate.

The Foolish bottom line
Air Products exhibits a clean dividend bill of health. Its moderate yield appears affordable given the company's low payout ratio. If Air Products can continue to grow its earnings and dividend at the impressive rates of the past, it might just be a dividend dynamo over the long term. To stay up to speed on Air Products' progress, or that of any other stock, add it to your stock watchlist. If you don't have one yet, you can create a free, personalized watchlist of your favorite stocks by clicking here.