As used in this chapter, the term “cooperative association” means any association in which farmers act together in processing, preparing for market, handling, and/or marketing the farm products of persons so engaged, and also means any association in which farmers act together in purchasing, testing, grading, processing, distributing, and/or furnishing farm supplies and/or farm business services: Provided, however, That such associations are operated for the mutual benefit of the members thereof as such producers or purchasers and conform to one or both of the following requirements: First. That no member of the association is allowed more than one vote because of the amount of stock or membership capital he may own therein; and Second. That the association does not pay dividends on stock or membership capital in excess of 8 per centum per annum. And in any case to the following: Third. That the association shall not deal in farm products, farm supplies, and farm business services with or for nonmembers in an amount greater in value than the total amount of such business transacted by it with or for members. All business transacted by any cooperative association for or on behalf of the United States or any agency or instrumentality thereof shall be disregarded in determining the volume of member and nonmember business transacted by such association.