ROLLINS INVESTMENT FUND
                                 P.O. Box 647
                               ATLANTA, GA 30301
                           TELEPHONE (404) 888-2750


                               September 8, 1998



HydroChem Industrial Services, Inc.
6210 Rothway
Suite 150
Houston, Texas 77040

Valley Systems, Inc.
11580 Lafayette Drive, NW
Canal Fulton, Ohio 44614

      Re:   Voting of Capital Stock of Valley Systems, Inc.

Gentlemen:

      Pursuant  to Section  1.5 of the Asset  Purchase  Agreement  entered  into
September  8, 1998,  by and  between  HydroChem  Industrial  Services,  Inc.,  a
Delaware  corporation  ("HydroChem"),  as buyer,  and Valley  Systems,  Inc.,  a
Delaware corporation ("Valley"), as seller (the "Agreement"),  please be advised
that  each of the  undersigned  hereby  irrevocably  agrees,  unless a  Superior
Takeover Proposal (as defined in the Agreement) then exists, to vote or cause to
be voted at the meeting of  stockholders  of Valley  Systems,  Inc.,  a Delaware
corporation ("Valley"),  to be held pursuant to such Section 1.5 (the "Meeting")
all of the shares of capital stock of Valley held  beneficially  or of record by
each of the  undersigned  and  entitled  to vote at the Meeting  (including  all
shares of common stock, par value $.01 per share (the "Common Shares"),  and all
shares of Series C  Preferred  Stock,  par value $.10 per share (the  "Preferred
Shares")) in favor of the approval  and adoption of the  Agreement,  the sale of
substantially  all of the  assets  of  Valley  pursuant  thereto,  and all other
transactions contemplated thereby.

      Each of the undersigned  hereby grants to HydroChem a right of first offer
to purchase  at any time which any of the  undersigned  determine,  prior to the
earlier of (i) the Meeting or (ii)  December 31, 1998, or sell any or all of the
Common  Shares,  at a price per  share of $3.00 and any or all of the  Preferred
Shares at a price per share of $100 (collectively the "Shares"), as follows:

      (i) Any of the undersigned desiring to sell all or a portion of its Shares
(the "Offeror") shall give written notice ("Notice of Sale") to HydroChem of its
desire to sell such Shares (or a portion thereof) (the "Offered Interest").



<PAGE>


HydroChem Industrial Services, Inc.
Valley Systems, Inc.
September     , 1998
Page 2

      (ii) HydroChem shall have the option  exercisable  until immediately prior
to the Meeting (the "Option  Period") to purchase all of the Offered Interest by
delivery of written notice of exercise of the option to the Offeror prior to the
expiration of the Option Period,  together with delivery,  by certified check or
wire transfer of immediately  available  funds, of the aggregate  purchase price
for the Shares to be so  purchased  in the amount of $3.00 per Common Share plus
$100 per Preferred Share.

      This letter shall not constitute a waiver of any other or further right of
the undersigned.

      Each of Valley and HydroChem may specifically  enforce the  obligations of
the undersigned contained herein. this letter my be executed in counterparts.

      This letter has been  executed  as of  September  8, 1998,  by each of the
undersigned.


ROLLINS INVESTMENT FUND                   ROLLINS HOLDING COMPANY, INC.


By:   /s/ R. Randall Rollins              By:   /s/ R. Randall Rollins
      R. Randall Rollins                        R. Randall Rollins
      General Partner and as co-executor of estate
      of O. Wayne Rollins and as Trustee  Title: President  
      of the several trusts listed on Attachment A
      hereto.



By:   /s/ Gary W. Rollins                
      Gary W. Rollins
      General Partner and as co-executor of estate
      of O. Wayne Rollins and as Trustee of the
      several trusts listed on Attachment A hereto.



<PAGE>


                                  ATTACHMENTS



R. Randall Rollins, Trustee of the
Richard R. Rollins, Jr. Qualified
Subchapter S Trust

R. Randall Rollins, Trustee of the
Pamela Renee Rollins Qualified
Subchapter S Trust

R. Randall Rollins, Trustee of the
Robert Wayne Rollins Qualified
Subchapter S Trust

R. Randall Rollins, Trustee of the
Timothy Curtis Rollins Qualified
Subchapter S Trust

R. Randall Rollins, Trustee of the
Amy Claudine Rollins Qualified
Subchapter S Trust

Gary W. Rollins, Trustee of the
Glen William Rollins Qualified
Subchapter S Trust

Gary W. Rollins, Trustee of the
Ruth Ellen Rollins Qualified
Subchapter S Trust

Gary W. Rollins, Trustee of the
Nancy Louise Rollins Qualified
Subchapter S Trust

Gary W. Rollins, Trustee of the
O. Wayne Rollins II Qualified
Subchapter S Trust