The answer depends on one of three things:
1.) Are you buying his share?
OR
2.) Are you selling your share to him?
OR
3.) Are you both selling out?
The reason I say this is because the valuation greatly depends on what undertaking is going on. For example, if you were to buy his share, that share would only be worth his percentage of ownership in the equipment, plus his wages for a set number of years. Generally speaking, this number usually ranges from 1 year to 15, depending on how long the business has been established and how financially strong it is. If the business is reputable and well established, there is an additional financial component for "goodwill" and the reputation associated with the business.
If you're both looking to sell out, a well established business can bring a considerable sum, even if it isn't particularly profitable. Suppose that both businesses combined generate $700,000 in sales, and out of that, you're able to pay you and your partner a salary of $35,000 per year. You would base the asking price off of a multiple of the cash flow available to pay salaries and reinvest in equipment.