<PAGE>
 
                                                                   Exhibit 10.11


                           STOCK REPURCHASE AGREEMENT

     THIS STOCK REPURCHASE AGREEMENT (the "Agreement"), entered into on January
2, 1998, is entered into by and between UNIT INSTRUMENTS, INC., a California
corporation (the "Company"), and JAMES C. LEVINSON AND MARILYN G. LEVINSON (the
"Levinsons"), individually and as general partners of the J & L LEVINSON
PARTNERSHIP (the "Shareholder").

                                   RECITALS:

     WHEREAS, the Shareholder is the owner of 368,475 shares of common stock,
$.15 par value ("Common Stock"), of the Company and the Levinsons desire to
cause the Shareholder to sell all of such shares (the "Repurchased Shares") to
the Company; and

     WHEREAS, the Levinsons hold options to purchase shares of the Company's
Common Stock, and the Levinsons desire that such options be terminated in
exchange for a cash payment from the Company; and

     WHEREAS, the Company desires to purchase the Repurchased Shares from the
Shareholder and terminate the Levinsons' options on the terms and conditions set
forth herein.

                                   AGREEMENT

     NOW THEREFORE, in consideration of the mutual promises and agreements
herein, and subject to the terms and conditions hereinafter set forth, the
parties hereby agree as follows:

     1.  REPURCHASE.  The Shareholder agrees to and does hereby sell, transfer
and convey to the Company the Repurchased Shares, free and clear of all liens,
claims and encumbrances, and the Company agrees to and does hereby purchase such
Repurchased Shares.  In consideration of the sale and transfer of such
Repurchased Shares and in full payment therefor, the Company shall pay to
Shareholder the purchase price of $12.25 per share, or Four Million Five Hundred
Thirteen Thousand Eight Hundred Eighteen and 75/100 Dollars ($4,513,818.75) in
the aggregate (the "Repurchase Price") payable at closing by wire transfer of
immediately available funds.  Concurrently with the sale and transfer of the
Repurchased Shares, the Company shall pay Fifty-Four Thousand Four Hundred
Seventy-Nine Dollars ($54,479) to the Levinsons by wire transfer of immediately
available funds in exchange for the termination of all outstanding options they
hold to acquire Common Stock of the Company (the "Options"), which termination
shall be deemed to occur automatically upon the making of such payment without
any further action by the Levinsons.

     2.  DELIVERIES.  Concurrently with the execution and delivery of this
Agreement, the Shareholder shall deliver to the Company all certificates
representing the Repurchased Shares, duly endorsed for transfer or accompanied
by duly executed stock powers transferring such Repurchased Shares to the
Company, and all of such Repurchased Shares shall be cancelled and returned to
the status of authorized but unissued shares.  Against delivery by Shareholder
of the stock certificates representing the Repurchased Shares, the Company shall
cause to be transferred to the Shareholder the Repurchase Price.
<PAGE>
 
     3.  REPRESENTATIONS AND WARRANTIES OF SHAREHOLDERS. Shareholder and each of
the Levinsons hereby represent and warrant to the Company as follows:

          3.1  LEGAL POWER.  Shareholder has the requisite legal power and
authority to enter into this Agreement, to sell and deliver the Repurchased
Shares and to perform its obligations hereunder.  Each of the Levinsons has the
legal right and capacity to enter into this Agreement and to perform its
obligations hereunder.  This Agreement is a valid and binding obligation of
Shareholder and each of the Levinsons, enforceable against such party in
accordance with its terms.  No further action is required to be taken by
Shareholder or either of the Levinsons, nor is it necessary for Shareholder or
either of the Levinsons to obtain any action, approval or consent by or from any
third person, governmental or other, to enable such party to enter into or
perform its obligations under this Agreement.

          3.2  TITLE TO SHARES.  Except for the Repurchased Shares and the
Options, neither the Shareholder nor either of the Levinsons owns, beneficially
or of record, any other securities of the Company or any rights to acquire
securities of the Company.  The Shareholder is the owner of the Repurchased
Shares and upon delivery of the Repurchased Shares and payment of the Repurchase
Price therefor as provided in this Agreement, the Company will have valid and
marketable title to the Repurchased Shares, free and clear of any liens,
encumbrances, security agreements, equities, charges, restrictions, claims and
any other adverse interests or defects in title of any kind or nature
whatsoever, except for restrictions on transfer imposed by federal or state
securities laws.  The Levinsons are the owners of the Options and have not sold
or assigned any interest therein to any other party.

          3.3  CONFLICTS.  The execution and delivery of this Agreement by the
Shareholder and the Levinsons and the performance by Shareholder and the
Levinsons of their respective obligations hereunder will not violate any
provision of any judicial or governmental decree, order, or judgment or conflict
with or violate any other agreement or understanding, written or oral, to which
Shareholder or either of the Levinsons is a party or by which any of such
parties or any of the Repurchased Shares are bound.

          3.4  ACCESS TO INFORMATION; INFORMED DECISION.  Shareholder and the
Levinsons have been provided access to and the opportunity to review all
material financial and business information regarding the Company necessary to
make a deliberate and informed decision to sell the Repurchased Shares to the
Company on the terms provided in this Agreement.  The partners of Shareholder
are sophisticated investors and have such knowledge and experience in financial
or business matters that they are capable of evaluating the economics, merits
and risks of the sale contemplated by this Agreement.  Such partners have
reviewed the economics, merits and risks of the transaction contemplated by this
Agreement, have reviewed all material information deemed by them necessary for
them to reach an informed decision on the sale herein, and are not relying on
the Company to furnish them any additional information.  Shareholder and the
Levinsons further acknowledge that the Company may enter into one or more
agreements for the merger or sale of the Company, which agreements may provide
for the payment of consideration to the Company's shareholders having a value in
excess of the Repurchase Price, and that the Repurchase Price may not bear any
relevance to the actual value of the Repurchased Shares or the Company.

                                       2
<PAGE>
 
     4.  REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

          4.1.  ORGANIZATION AND EXISTENCE; AUTHORITY.  The Company is a
corporation duly organized, validly existing and in good standing under the laws
of the State of California, and has all requisite corporate power to carry on
its business as now conducted.  The Company has the corporate power and
authority to enter into this Agreement and perform its obligations hereunder.
The execution, delivery, and performance by the Company of this Agreement and
the transactions contemplated hereby have been duly authorized and approved by
the Board of Directors of the Company in accordance with the Articles of
Incorporation and Bylaws of the Company and California law, and no further
corporate action is necessary on the part of the Company with respect thereto.
This Agreement is a valid and binding obligation of the Company, enforceable
against it in accordance with its terms.  No further action is required to be
taken by the Company, nor is it necessary for the Company to obtain any action,
approval or consent by or from any third person, governmental or other, to
enable it to enter into or perform its obligations under this Agreement.

          4.2  NO CONFLICTS.  The execution and delivery of this Agreement and
performance of the Company's obligations hereunder do not and will not violate
any provision of any judicial or governmental decree, order, or judgment or
conflict with, or result in a breach of or constitute a default under, the
Articles of Incorporation or Bylaws of the Company or any agreement or
instrument to which the Company is a party or by which it is bound.

          4.3  COMPLIANCE WITH CALIFORNIA CORPORATIONS CODE.  The repurchase of
the Repurchased Shares by the Company will be in full compliance with all of the
provisions of the California Corporations Code, including, without limitation,
Chapter 5 thereof.

     5.  RESIGNATION.  Mr. James C. Levinson hereby resigns as a Director of the
Company and as a director of each subsidiary of the Company of which he is a
director, effective immediately, and the Company and each such subsidiary hereby
accept such resignations.  Following the date hereof, neither the Company nor
Mr. Levinson shall represent to any person or entity that Mr. Levinson is a
director of the Company or any such subsidiary.  Mr. Levinson shall maintain the
confidentiality of, and shall not use, the Company's non-public proprietary
information, and shall promptly return any and all such materials in his
possession to the Company.  Mr. Levinson will not waive any evidentiary or
testimonial privileges relating to the Company, which Mr. Levinson may otherwise
waive, without the consent of the Company, unless he is required to do so by
judicial order or unless suit is brought against him by the Company.

     6.  STANDSTILL.  Shareholder and each of the Levinsons agrees that, for a
period of two (2) years from the date of this Agreement, neither such party nor
any of its affiliates will, without the prior written consent of the other
party; (i) acquire, offer to acquire, or agree to acquire, directly or
indirectly, by purchase or otherwise, any voting securities or direct or
indirect rights to acquire any voting securities of the Company; (ii) make, or
in any way participate in, directly or indirectly, any "solicitation" of
"proxies" (as such terms are used in the rules of the Securities Exchange
Commission) to vote, or seek to advise or influence any person or entity with
respect to the voting of, any voting securities of the Company; (iii) make any
public announcement with respect to, or submit a proposal for, or offer of (with
or without conditions) any merger, business combination, recapitalization,
restructuring, liquidation or other extraordinary transaction involving the
Company or its securities or assets; (iv) form, join or in any way participate
in a "group" (as defined in Section 

                                       3
<PAGE>
 
13(d)(3) of the Securities Exchange Act of 1934, as amended) in connection with
any of the foregoing; (v) enter into any discussions or arrangements with any
third party with respect to any of the foregoing; or (vi) request publicly the
other party or any of its Representatives, directly or indirectly, to amend or
waive any provision of this paragraph. Each of such parties will promptly advise
the Company of any inquiry or proposal made to such party with respect to any of
the foregoing.

     7.  NON-COMPETITION; NON-SOLICITATION.

          7.1  NON-COMPETITION.  Shareholder and each of the Levinsons
covenants, that for a period of three (3) consecutive years commencing on the
date hereof, such party shall not directly, or indirectly through one or more
other persons or entities, engage in, or have any financial or other interests
in or provide assistance to any person, firm, corporation or business that
engages in, any activity which is the same as or competitive with the business
engaged in by the Company as of the date hereof (the "Business"), in, from, at
or into (a) any of the states of the United States of America or the District of
Columbia or (b) any of the countries, territories or areas of the world.
Notwithstanding the foregoing, nothing contained in this Agreement shall prevent
or otherwise limit such party from holding, for investment purposes only, no
more than one percent (1%) of any class of equity securities of a company
engaged in activities that are competitive with the Business if such class of
equity securities is traded on a national securities exchange or on the NASDAQ
National Market System.

          7.2  NON-SOLICITATION.  Shareholder and each of the Levinsons agree
that, for a period of one (1) year from the date of this Agreement, it will not,
directly or through any of its representatives or affiliates, solicit for
employment or hire any employee of the Company or any of its subsidiaries.

     8.  NON-DISPARAGEMENT.  Each party shall refrain from making, orally or in
writing, any statement of a disparaging or critical nature regarding the other
party to any person, including but not limited to any past, present or
prospective employees or customers of such party, except to the extent that
either party is required to provide testimony under oath pursuant to a subpoena
or other legal process, and neither party shall issue any press release or other
public statement or comment concerning this agreement or the transactions
contemplated by this agreement except as required by law or with the prior
written consent of the other party.  Neither party shall take any action,
directly or indirectly, with the intent of causing, creating or instigating any
third party claim concerning the transactions contemplated by this Agreement.

     9.  INDEMNIFICATION.

          9.1  INDEMNIFICATION BY THE COMPANY.  The Company shall indemnify,
defend and hold harmless Shareholder and the Levinsons from and against claims,
losses, liabilities, damages, costs and expenses, including, without limitation,
attorneys' fees (hereafter "Damages") arising out of or in connection with (a)
any breach by the Company of any of its representations, warranties or covenants
contained in this Agreement, (b) the purchase and sale of the Repurchased Shares
and the termination and purchase of the Options pursuant to this Agreement, or
(c) Mr. Levinson's activities in his capacity as a director or officer of the
Company or any of its subsidiaries through and including the date hereof.  Such
indemnification right shall include, without 

                                       4
<PAGE>
 
limitation, the costs, expenses and attorneys' fees of enforcing such
indemnification against the Company. The Company shall pay directly or reimburse
the Shareholder or the Levinsons for any costs, expenses, and attorneys' fees,
as they are incurred, in advance of the final disposition of any matter as to
which the Shareholder or the Levinsons would be entitled to be indemnified
hereunder.

          9.2  INDEMNIFICATION BY SHAREHOLDER.  Shareholder and the Levinsons
shall indemnify, defend and hold harmless the Company from and against all
Damages incurred by the Company as a result of any breach by the Shareholder or
either of the Levinsons of any of such party's representations, warranties or
covenants contained in this Agreement.  Such indemnification right shall
include, without limitation, the costs, expenses and attorneys' fees of
enforcing such indemnification against the Shareholder or either of the
Levinsons.  The Shareholder or the Levinsons shall pay directly or reimburse the
Company for any costs, expenses, and attorneys' fees, as they are incurred, in
advance of the final disposition of any matter as to which the Company would be
entitled to be indemnified hereunder.

          9.3  PROCEDURE.  In the event a party believes that it is entitled to
indemnification hereunder (such party, the "Indemnitee"), the Indemnitee shall
give written notice to the other party (the "Indemnitor") indicating in
reasonable detail the basis on which the claim for indemnification is based and,
if known, the amount of such claim.  Such notice shall be given promptly after
the Indemnitee becomes aware of the facts on which such claim is based.  Upon
receipt of any notice of a claim for indemnification hereunder based on a claim
by a third party against Indemnitee, Indemnitor shall have the right to assume
the defense of such third party claim by notifying Indemnitee of its election to
do so within thirty (30) days of Indemnitee's notice to Indemnitor of such
claim; provided, however, that in making such election, Indemnitor must confirm
in writing that it will indemnify Indemnitee from all Damages related to such
claim; and provided further that Indemnitee shall have the right to reasonably
approve counsel selected by Indemnitor to defend such claim; and provided
further that the Indemnitee shall have the right to its own counsel selected by
Indemnitee (the costs of which shall be borne by Indemnitor) in the event the
interests of the Indemnitor (or any of its officers or directors in the case of
the Company) differs from or is in conflict with the interests of the
Indemnitee.  Nothing herein shall prevent the Indemnitee from retaining its own
counsel to participate in such defense so long as the costs of such counsel are
borne by the Indemnitee.  If Indemnitor declines to assume the defense of any
such third party claim, Indemnitee may undertake the defense of such claim
without waiving any of its rights to seek indemnification for all Damages
related thereto from Indemnitor; provided, however, that Indemnitee may not
settle any such claim without Indemnitor's prior consent, which consent may not
be unreasonably withheld.  If the Indemnitor declines to assume the defense of
any such third party claim, the Indemnitor shall nevertheless pay directly or
reimburse the Indemnitee for any costs, expenses and attorneys' fees, as they
are incurred, in advance of the final disposition of such third party claim.
Regardless of which party elects to defend any such third party claim,
Indemnitee and Indemnitor shall render reasonable assistance and cooperation to
each other in connection with defending such claim and shall keep each other
reasonably apprised of the status of any proceedings relating to such claim.
The indemnification provisions of Section 9.1 and 9.2 are not mutually
exclusive, and both such provisions may apply with respect to a given claim.

                                       5
<PAGE>
 
     10.  GENERAL RELEASE OF CLAIMS.

          10.1  BY THE LEVINSONS.  In exchange for this Agreement and the
consideration provided in Section 1 above, and except for claims arising under
or in connection with (i) this Agreement, (ii) the indemnification provisions of
California law or the Articles of Incorporation or Bylaws or indemnification
agreements of the Company that are intended to cover former officers or
directors of the Company or any of its subsidiaries, (iii) the directors and
officers insurance of the Company, or (iv) James C. Levinson's supplemental
pension in the amount of $1,833.33 per month for life, the Shareholder and each
of the Levinsons each hereby waives and releases all claims, known and unknown,
which such party has or might otherwise have against the Company, its related
entities and its officers, directors, employees, agents, insurers,
representatives, successors and assigns.

          10.2  BY THE COMPANY.  In exchange for this Agreement, and except for
claims arising under or in connection with (i) this Agreement or that certain
Stock Repurchase Agreement of even date herewith among the Company and the
parties listed on Schedule 1 thereto, or (ii) the failure of Mr. Levinson to
comply with his express obligations (if any) relating to the items referenced in
clauses (ii) and (iii) of Section 10.1 above, the Company hereby waives and
releases all claims, known and unknown, which it has or might otherwise have
against the Shareholder or either of the Levinsons or their children,
grandchildren, heirs and successors.

          10.3  UNKNOWN CLAIMS.  IT IS FURTHER UNDERSTOOD AND AGREED that as a
condition of this Agreement, all rights under Section 1542 of the Civil Code of
the State of California are expressly waived by Shareholder, the Levinsons and
the Company.  Such Section reads as follows:

          "A general release does not extend to claims which the creditor does
          not know or suspect to exist in his favor at the time of executing the
          release, which if known by him must have materially affected his
          settlement with the debtor."

Notwithstanding Section 1542, and for the purpose of implementing a full and
complete release and discharge, Shareholder, the Levinsons and the Company
expressly acknowledge that this Agreement is intended to include and does
include in its effect, without limitation, all claims which any such party does
not know or suspect to exist in its favor against another at the time of
execution hereof, and that, except as expressly provided herein, this Agreement
expressly contemplates the extinguishment of all such claims.

     11.  MISCELLANEOUS.

          11.1  NO ASSIGNMENT.  Neither party may assign this Agreement or any
rights or obligations hereunder to any other person or entity, without the prior
written consent of the other parties hereto.

          11.2  SURVIVAL.  The representations, warranties, covenants and
agreements made herein shall survive any investigation made by any party and the
closing of the transactions contemplated hereby.

                                       6
<PAGE>
 
          11.3  SUCCESSORS AND ASSIGNS.  The provisions hereof shall inure to
the benefit of, and be binding upon, the successors, assigns, heirs, executors
and administrators of the parties hereto.

          11.4  ENTIRE AGREEMENT; AMENDMENT.  This Agreement and the other
documents delivered pursuant hereto constitute the full and entire understanding
and agreement between the parties with regard to the subject matter hereof, and
no party shall be liable or bound to any other party in any manner by any
warranties, representations or covenants except as specifically set forth
herein.  Except as expressly provided herein, neither this Agreement nor any
term hereof may be amended, waived, discharged or terminated other than by a
written instrument signed by the party against whom enforcement of any such
amendment, waiver, discharge or termination is sought.

          11.5  NOTICES, ETC.  All notices and other communications required or
permitted hereunder shall be in writing, signed by the party giving the notice
and delivered personally, by overnight delivery service or by registered or
certified mail to the address of the party set forth on the signature page
hereto.  Either party may at any time change the address to which notice shall
be mailed by giving written notice of such change to the other party.

          11.6  SEVERABILITY.  In the event that any provision of this Agreement
becomes or is declared by a court of competent jurisdiction to be illegal,
unenforceable or void, this Agreement shall continue in full force and effect
without said provision; provided that no such severability shall be effective if
it materially changes the economic benefit of this Agreement to any party.

          11.7  GOVERNING LAW.  This Agreement shall be governed by and
construed in accordance with the laws of the State of California without regard
to any conflict of law provisions.

          11.8  COUNTERPARTS.  This Agreement may be executed in counterparts,
and by facsimile transmission, all of which together shall constitute one and
the same instrument.

                                       7
<PAGE>
 
     IN WITNESS WHEREOF, the undersigned have executed this Repurchase Agreement
as of the date first written above.

                                       "Shareholder"


Address of Shareholder and Levinsons:  J & L LEVINSON PARTNERSHIP

100 Anchor Drive, Suite 460
Key Largo, Florida  33037
                                       By: ____________________________________
                                           James C. Levinson, individually and 
with a copy to:                            as a General Partner


Carl Cohen, Esq.
Buchanan Ingersoll                     By: _____________________________________
301 Grant Street, 20th Floor               Marilyn G. Levinson, individually and
Pittsburgh, Pennsylvania  15219            as a General Partner 





                                       "Company"

Address of Company:                    UNIT INSTRUMENTS, INC.,
                                       a California corporation
22600 Savi Ranch Parkway
Yorba Linda, California  92687
                                       By: _____________________________________
                                           Gary N. Patten, Chief Financial 
                                           Officer

                                       8
<PAGE>
 
                           STOCK REPURCHASE AGREEMENT

     THIS STOCK REPURCHASE AGREEMENT (the "Agreement"), entered into on January
2, 1998, is entered into by and between UNIT INSTRUMENTS, INC.,  a California
corporation (the "Company"), and the parties listed on Schedule 1 hereto (the
"Shareholders").

                                   RECITALS:

     WHEREAS, the Shareholders own an aggregate of 43,740 shares of common
stock, $.15 par value ("Common Stock"), of the Company and the Shareholders
desire to sell all of such shares (the "Repurchased Shares") to the Company; and

     WHEREAS, the Company desires to purchase the Repurchased Shares from such
persons on the terms and conditions set forth herein.

                                   AGREEMENT

     NOW THEREFORE, in consideration of the mutual promises and agreements
herein, and subject to the terms and conditions hereinafter set forth, the
parties hereby agree as follows:

     1.  REPURCHASE.  Each of the Shareholders agrees severally to and does
hereby sell, transfer and convey to the Company the Repurchased Shares set forth
opposite such Shareholder's name on Schedule 1 hereto, free and clear of all
liens, claims and encumbrances, and the Company agrees to and does hereby
purchase such Repurchased Shares.  In consideration of the sale and transfer of
such Repurchased Shares and in full payment therefor, the Company shall pay to
each such Shareholder the purchase price of Twelve and 25/100 Dollars ($12.25)
per Repurchased Share (the "Repurchase Price") payable at closing by wire
transfer of immediately available funds.  Notwithstanding the foregoing, the
Company shall not have any obligation to purchase the Repurchased Shares unless
and until the J&L Levinson Partnership shall have delivered the Partnership's
Shares in accordance with Section 2 of that certain Stock Repurchase Agreement
of even date herewith among the Company and James and Marilyn Levinson, as
partners of the J&L Levinson Partnership.

     2.  DELIVERIES.  Concurrently with the execution and delivery of this
Agreement, each Shareholder shall deliver to the Company all certificates
representing the Repurchased Shares held by it, duly endorsed for transfer or
accompanied by duly executed stock powers (or take such other steps as are
necessary for) transferring such Repurchased Shares to the Company, and all of
such Repurchased Shares shall be cancelled and returned to the status of
authorized but unissued shares.  Against delivery by Shareholder of the stock
certificates representing the Repurchased Shares, the Company shall cause to be
transferred to the Shareholder the Repurchase Price for such Shareholder's
Repurchased Shares.

     3.  REPRESENTATIONS AND WARRANTIES OF SHAREHOLDERS.  Each Shareholder
hereby represents and warrants to the Company as follows:

          3.1  LEGAL POWER.  Each Shareholder that is an individual has the
legal right and capacity to enter into this Agreement, to sell and deliver such
Shareholder's Repurchased Shares and 

                                       9
<PAGE>
 
to carry out and perform its obligations hereunder. Each other Shareholder has
the requisite legal power and authority to enter into this Agreement, to sell
and deliver such Shareholder's Repurchased Shares and to carry out and perform
its obligations hereunder. This Agreement is a valid and binding obligation of
such Shareholder, enforceable against such Shareholder in accordance with its
terms. No further action is required to be taken by such Shareholder, nor is it
necessary for such Shareholder to obtain any action, approval or consent by or
from any third person, governmental or other, to enable such Shareholder to
enter into or perform its obligations under this Agreement.

          3.2  TITLE TO SHARES.  Such Shareholder is the owner of the
Repurchased Shares set forth opposite such Shareholder's name on Schedule 1
hereto, which represents all of the securities of the Company currently owned,
beneficially or of record, by such Shareholder, and upon delivery of such
Shareholder's Repurchased Shares and payment of the Repurchase Price therefor as
provided in this Agreement, such Shareholder will convey to the Company valid
and marketable title to such Repurchased Shares, free and clear of any liens,
encumbrances, security agreements, equities, charges, restrictions, claims and
any other adverse interests or defects in title of any kind or nature
whatsoever, except for restrictions on transfer imposed by federal or state
securities laws.

          3.3  CONFLICTS.  Such Shareholder's execution and delivery of this
Agreement and the performance by such Shareholder of its obligations hereunder
will not violate any provision of any judicial or government decree, order or
judgment or conflict with or violate any other agreement or understanding,
written or oral, to which such Shareholder is a party or by which any of the
Repurchased Shares are bound.

          3.4  ACCESS TO INFORMATION; INFORMED DECISION. Such Shareholder has
been provided access to and the opportunity to review all material financial and
business records of the Company necessary to make a deliberate and informed
decision to sell such Shareholder's Repurchased Shares to the Company on the
terms provided in this Agreement. Such Shareholder, either alone or with its
representatives, is a sophisticated investor and has such knowledge and
experience in financial or business matters that it is capable of evaluating the
economics, merits and risks of the sale contemplated by this Agreement. Such
Shareholder has reviewed the economics, merits and risks of the transaction
contemplated by this Agreement, has reviewed all material information deemed by
it necessary for it to reach an informed decision on the sale herein, and is not
relying on the Company to furnish it any additional information. Such
Shareholder further acknowledges that the Company may enter into one or more
agreements for the merger or sale of the Company, which agreements may provide
for the payment of consideration to the Company's shareholders having a value in
excess of the Repurchase Price, and that the Repurchase Price may not bear any
relevance to the actual value of the Repurchased Shares or the Company.

     4.  REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

          4.1  ORGANIZATION AND EXISTENCE; AUTHORITY.  The Company is a
corporation duly organized, validly existing and in good standing under the laws
of the State of California, and has all requisite corporate power to carry on
its business as now conducted.  The Company has the corporate power and
authority to enter into this Agreement and perform its obligations hereunder.
The execution, delivery, and performance by the Company of this Agreement and
the transactions contemplated hereby have been duly authorized and approved by
the Board of Directors of the Company in accordance with the Articles of
Incorporation and Bylaws of the Company and 

                                       10
<PAGE>
 
California law and no further corporate action is necessary on the part of the
Company with respect thereto. This Agreement is a valid and binding obligation
of the Company, enforceable against it in accordance with its terms. No further
action is required to be taken by the Company, nor is it necessary for the
Company to obtain any action, approval or consent by or from any third person,
governmental or other, to enable it to enter into or perform its obligations
under this Agreement.

          4.2  NO CONFLICTS.  The execution and delivery of this Agreement and
performance of the Company's obligations hereunder do not and will not violate
any provision of any judicial or governmental decree, order, or judgment or
conflict with, or result in a breach of or constitute a default under, the
Articles of Incorporation or Bylaws of the Company or any agreement or
instrument to which the Company is a party or by which it is bound.

          4.3  COMPLIANCE WITH CALIFORNIA CORPORATIONS CODE.  The repurchase of
the Repurchased Shares by the Company will be in full compliance with all of the
provisions of the California Corporations Code, including, without limitation,
Chapter 5 thereof.

     5.  STANDSTILL.  Each Shareholder agrees that, for a period of two (2)
years from the date of this Agreement, neither it nor any of its affiliates
will, without the prior written consent of the other party; (i) acquire, offer
to acquire, or agree to acquire, directly or indirectly, by purchase or
otherwise, any voting securities or direct or indirect rights to acquire any
voting securities of the Company; (ii) make, or in any way participate in,
directly or indirectly, any "solicitation" of "proxies" (as such terms are used
in the rules of the Securities Exchange Commission) to vote, or seek to advise
or influence any person or entity with respect to the voting of, any voting
securities of the Company; (iii) make any public announcement with respect to,
or submit a proposal for, or offer of (with or without conditions) any merger,
business combination, recapitalization, restructuring, liquidation or other
extraordinary transaction involving the Company or its securities or assets;
(iv) form, join or in any way participate in a "group" (as defined in Section
13(d)(3) of the Securities Exchange Act of 1934, as amended) in connection with
any of the foregoing; (v) enter into any discussions or arrangements with any
third party with respect to any of the foregoing; or (vi) request publicly the
other party or any of its Representatives, directly or indirectly, to amend or
waive any provision of this paragraph.  Each Shareholder will promptly advise
the Company of any inquiry or proposal made to such party with respect to any of
the foregoing.

     6.  INDEMNIFICATION.

          6.1  INDEMNIFICATION BY THE COMPANY.  The Company shall indemnify,
defend and hold harmless each Shareholder from and against all claims, losses,
liabilities, damages, costs and expenses, including, without limitation,
attorneys' fees (hereafter "Damages") arising out of or in connection with (a)
any breach by the Company of any of its representations, warranties or covenants
contained in this Agreement, or (b) the transactions contemplated by this
Agreement.  Such indemnification right shall include, without limitation, the
costs, expenses, and attorneys' fees of enforcing such indemnification against
the Company.  The Company shall pay directly or reimburse each Shareholder for
any costs, expenses, and attorneys' fees, as they are incurred, in advance of
the final disposition of any matter as to which such Shareholder would be
entitled to be indemnified hereunder.

                                       11
<PAGE>
 
          6.2  INDEMNIFICATION BY SHAREHOLDER.  Each Shareholder shall
indemnify, defend and hold free and harmless the Company from and against all
Damages incurred by the Company as a result of any breach by such Shareholder of
any of his representations, warranties or covenants contained in this Agreement.
Such indemnification right shall include, without limitation, the costs,
expenses and attorneys' fees of enforcing such indemnification against each
Shareholder.  Each Shareholder shall pay directly or reimburse the Company for
any costs, expenses, and attorneys' fees, as they are incurred, in advance of
the final disposition of any matter as to which the Company would be entitled to
be indemnified hereunder.

          6.3  PROCEDURE.  In the event a party believes that it is entitled to
indemnification hereunder (such party, the "Indemnitee"), the Indemnitee shall
give written notice to the other party (the "Indemnitor") indicating in
reasonable detail the basis on which the claim for indemnification is based and
the amount, if known, of such claim.  Such notice shall be given promptly after
the Indemnitee becomes aware of the facts on which such claim is based.  Upon
receipt of any notice of a claim for indemnification hereunder based on a claim
by a third party against Indemnitee, Indemnitor shall have the right to assume
the defense of such third party claim by notifying Indemnitee of its election to
do so within thirty (30) days of Indemnitee's notice to Indemnitor of such
claim; provided, however, that in making such election, Indemnitor must confirm
in writing that it will indemnify Indemnitee from all Damages related to such
claim; and provided further that Indemnitee shall have the right to reasonably
approve counsel selected by Indemnitor to defend such claim; and provided
further that the Indemnitee shall have the right to its own counsel selected by
Indemnitee (the cost of which shall be borne by Indemnitor) in the event the
interests of the Indemnitor (or any of its officers or directors in the case of
the Company) differs from or is in conflict with the interests of the
Indemnitee.  Nothing herein shall prevent the Indemnitee from retaining its own
counsel to participate in such defense so long as the costs of such counsel are
borne by the Indemnitee.  If Indemnitor declines to assume the defense of any
such third party claim, Indemnitee may undertake the defense of such claim
without waiving any of its rights to seek indemnification for all Damages
related thereto from Indemnitor; provided, however, that Indemnitee may not
settle any such claim without Indemnitor's prior consent, which consent may not
be unreasonably withheld.  If the Indemnitor declines to assume the defense of
any such third party claim, the Indemnitor shall nevertheless pay directly or
reimburse the Indemnitee for any costs, expenses and attorneys' fees, as they
are incurred, in advance of the final disposition of such third party claim.
Regardless of which party elects to defend any such third party claim,
Indemnitee and Indemnitor shall render reasonable assistance and cooperation to
each other in connection with defending such claim and shall keep each other
reasonably apprised of the status of any proceedings relating to such claim.

     7.  GENERAL RELEASE OF CLAIMS.

          7.1  BY SHAREHOLDER.  In exchange for this Agreement and the
consideration provided in Section 1 above, and except for claims arising under
or in connection with this Agreement, each Shareholder hereby waives and
releases all claims, known and unknown, which such Shareholder has or might
otherwise have against the Company, its related entities and its officers,
directors, employees, agents, insurers, representatives, successors and assigns.

          7.2  BY THE COMPANY.  In exchange for this Agreement, and except for
claims arising under or in connection with this Agreement, the Company hereby
waives and releases all 

                                       12
<PAGE>
 
claims, known and unknown, which it has or might otherwise have against any of
the Shareholders or their heirs and successors.

          7.3  UNKNOWN CLAIMS.  IT IS FURTHER UNDERSTOOD AND AGREED that as a
condition of this Agreement, all rights under Section 1542 of the Civil Code of
the State of California are expressly waived by each Shareholder and the
Company.  Such Section reads as follows:

          "A general release does not extend to claims which the creditor does
          not know or suspect to exist in his favor at the time of executing the
          release, which if known by him must have materially affected his
          settlement with the debtor."

Notwithstanding Section 1542, and for the purpose of implementing a full and
complete release and discharge, each Shareholder and the Company expressly
acknowledge that this Agreement is intended to include and does include in its
effect, without limitation, all claims which any such party does not know or
suspect to exist in its favor against another at the time of execution hereof,
and that, except as expressly provided herein, this Agreement expressly
contemplates the extinguishment of all such claims.

     8.  MISCELLANEOUS.

          8.1  NO ASSIGNMENT.  Neither party may assign this Agreement or any
rights or obligations hereunder to any other person or entity, without the prior
written consent of the other parties hereto.

          8.2  SURVIVAL.  The representations, warranties, covenants and
agreements made herein shall survive any investigation made by any party and the
closing of the transactions contemplated hereby.

          8.3  SUCCESSORS AND ASSIGNS.  The provisions hereof shall inure to the
benefit of, and be binding upon, the successors, assigns, heirs, executors and
administrators of the parties hereto.

          8.4  ENTIRE AGREEMENT; AMENDMENT.  This Agreement and the other
documents delivered pursuant hereto constitute the full and entire understanding
and agreement between the parties with regard to the subject matter hereof, and
no party shall be liable or bound to any other party in any manner by any
warranties, representations or covenants except as specifically set forth
herein.  Except as expressly provided herein, neither this Agreement nor any
term hereof may be amended, waived, discharged or terminated other than by a
written instrument signed by the party against whom enforcement of any such
amendment, waiver, discharge or termination is sought.

          8.5  NOTICES, ETC.  All notices and other communications required or
permitted hereunder shall be in writing, signed by the party giving the notice
and delivered personally, by overnight delivery service or by registered or
certified mail to the address of the party set forth on the signature page(s)
hereto.  Either party may at any time change the address to which notice shall
be mailed by giving written notice of such change to the other party.

                                       13
<PAGE>
 
          8.6  SEVERABILITY.  In the event that any provision of this Agreement
becomes or is declared by a court of competent jurisdiction to be illegal,
unenforceable or void, this Agreement shall continue in full force and effect
without said provision; provided that no such severability shall be effective if
it materially changes the economic benefit of this Agreement to any party.

          8.7  GOVERNING LAW.  This Agreement shall be governed by and construed
in accordance with the laws of the State of California without regard to any
conflict of law provisions.

          8.8  COUNTERPARTS.  This Agreement may be executed in counterparts,
and by facsimile transmission, all of which together shall constitute one and
the same instrument.  In the event that a Shareholder fails to execute and
deliver a counterpart of this Agreement by February 28, 1998, such Shareholder
shall be deemed deleted from this Agreement, and the Company shall have no
obligation to purchase any of the Repurchased Shares held by such Shareholder
whether or not such counterpart is subsequently delivered by such Shareholder.

     IN WITNESS WHEREOF, the undersigned have executed this Stock Repurchase
Agreement as of the date first written above.


                                   "Company"

Address of Company:                UNIT INSTRUMENTS, INC.,
                                   a California corporation

22600 Savi Ranch Parkway
Yorba Linda, California  92687
                                   By: ________________________________________
                                       Gary N. Patten, Chief Financial Officer



                      [SIGNATURES CONTINUED ON NEXT PAGE]

                                       14
<PAGE>
 
  The undersigned Seller agrees to be bound by all of the provisions of the
foregoing Stock Repurchase Agreement dated January 2, 1998 among Unit
Instruments, Inc. and the shareholders listed on Schedule 1 hereto.


Dated: ___________, 1998               ______________________________________
                                       Name of Shareholder


                                       ______________________________________
                                       Signature


                                       _________________________
                                       No. of Shares Owned


                                       ______________________________________

                                       ______________________________________ 
                                       Address of Shareholder

                                       15
<PAGE>
 
                                 SCHEDULE 1 TO
                           Stock Repurchase Agreement
<TABLE>
<CAPTION>
 
 
                                                                Total       
                                               No. of         Purchase      
           Shareholder                         Shares           Price       
-------------------------------------          ------        -----------    
<S>                                            <C>           <C>            
Jane L. Kerschner                               7,457        $ 91,348.25    
                                                                            
Jane L. Kerschner as Custodian for              1,010        $ 12,372.50    
Jill B. Romansky                                                            
                                                                            
Jane L. Kerschner as Custodian for              1,010        $ 12,372.50    
Kathryn M. Romansky                                                         
                                                                            
Jane L. Kerschner as Custodian for              1,010        $ 12,372.50    
Kira S. Romansky                                                            
                                                                            
Andrea L. Stern                                 1,976        $ 24,206.00    
                                                                            
Andrea L. Stern as Custodian for               11,641        $142,602.25    
Alexander F. Henley                                                         
                                                                            
Andrea L. Stern as Custodian for                6,257        $ 76,648.25    
Marion H. Henley                                                            
                                                                            
Peter G. Levinson                               2,710        $ 33,197.50    
                                                                            
PNC Bank as Trustee for the                     3,739        $ 45,802.75    
Sarah E. Levinson Irrevocable                                               
Educational Trust                                                           
                                                                            
PNC Bank as Trustee for the                     3,313        $ 40,584.25    
Jacob J. Levinson Irrevocable                                               
Educational Trust                                                           
                                                                            
PNC Bank as Trustee for the                     2,607        $ 31,935.75    
Benjamin A. Levinson Irrevocable                                            
Educational Trust                                                           
                                                                            
Peter G. Levinson as Custodian for              1,010        $ 12,372.50    
Taylor G. Levinson                                                          
                                                                            
TOTAL                                          43,740        $535,815.00    
</TABLE>

                                       16