Of course, past performance is no guarantee of future results. But since we can’t peek into the future of Accela, which was just acquired by Boston-based private equity firm Berkshire Partners, let’s take a look at the past anyway. The main strategy of private equity is to acquire a majority stake in a company, increase the company’s value, and then sell it to somebody else — in the form of an initial public offering, or perhaps to another private group. The way a private equity investor like Berkshire increases the value of its portfolio companies, however, is not always obvious.