EXHIBIT 5.1
 
September 18, 1995
 
Vallen Corporation
13333 Northwest Freeway
Houston, Texas 77040
 
Ladies and Gentlemen:
 
  We have acted as counsel for Vallen Corporation (the "Company") in connection
with the registration and proposed sale of an aggregate of 128,754 shares (the
"Shares") of Common Stock, par value $.50 per share, of the Company ("Common
Stock"), all as described in the Company's Registration Statement on Form S-3
filed with the Securities and Exchange Commission under the Securities Act of
1933, as amended ("Registration Statement"). In such capacity, we have
familiarized ourselves with the Articles of Incorporation, as amended and
restated, the Bylaws of the Company, as amended and restated, and have examined
all statutes and other records, instruments and documents pertaining to the
Company that we have deemed necessary to examine for the purposes of this
opinion.
 
  Based upon our examination as aforesaid, we are of the opinion that:
 
    1. The Company is a corporation duly incorporated, validly existing and
  in good standing under the laws of the State of Texas; and
 
    2. The Shares are duly authorized, validly issued, fully paid and
  nonassessable shares of the Common Stock.
 
  We hereby consent to the filing of this opinion with the Securities and
Exchange Commission as an exhibit to the Registration Statement and to the use
of our name in the Registration Statement under the caption "Legal Opinions."
 
                                     Very truly yours,
 
                                     /s/ Mayor, Day, Caldwell & Keeton, L.L.P.
 
                                     MAYOR, DAY, CALDWELL & KEETON, L.L.P.