<PAGE>
 
For Bank Use Only                                                          10.18

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                                                               /s/ Dan Alstolfi
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LIS NO.              LOAN NO.             BORROWER             APPROVAL 
                                                               SIGNATURE

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                          COMMERCIAL PROMISSORY NOTE         [LOGO OF CORESTATES
                                                                APPEARS HERE]

   $ 150,000.00                                               September 28, 1994
   -------------------------                               ---------------------


       FOR VALUE RECEIVED, each of the undersigned, jointly and severally if
   more than one (hereinafter collectively referred to as "Borrower"), promises
   to pay to the order of CORESTATES BANK, N.A.*, a national banking association
   (the "Bank"), at any of its banking offices in Pennsylvania, the principal
   amount of One Hundred Fifty Thousands and --------00/100 DOLLARS, in lawful
             ----------------------------------------------
   money of the United States, plus interest, to be paid as follows:

Said principal shall be payable in 60 consecutive equal monthly installments, 
each in the amount of $2,500.00, payable on the first day of each month 
beginning on November 1, 1994, plus interest on each said date fixed for 
payments in reduction of principal. Interest shall accrue at a per annum rate 
equal to 1% in excess of the Prime Rate. The amount of the final payment will 
be that amount which is necessary to pay in full all of the outstanding 
principal plus accrued and unpaid interest on this Note on the date thereof.

ADDITIONAL TERMS OF THIS NOTE - Each of the following provisions shall apply to 
this Note, to any extension or modification hereof and to the indebtedness 
evidenced hereby, except as otherwise expressly stated above or in a separate 
writing signed by Bank and Borrower.

INTEREST - Interest shall be calculated on the basis of a 360-day year and shall
be charged for the actual number of days elapsed. Accrued interest shall be 
payable monthly. Accrued interest shall also be payable when the entire 
principal balance of this Note becomes due and payable (whether by demand, 
stated maturity or acceleration) or, if earlier, when such principal balance is
actually paid to Bank. If the rate at which interest accrues is based on the 
"Prime Rate", that term is defined as the rate of interest for loans established
by Bank from time to time as its prime rate. Said per annum rate of interest 
shall change each time Bank's prime rate shall change, effective on and as of 
the date of the change. Interest shall accrue on each disbursement hereunder 
from the date such disbursement is made by Bank, provided, however, that to the 
extent this Note represents a replacement, substitution, renewal or refinancing 
of existing indebtedness, interest shall accrue from the date hereof. Interest 
shall accrue on the unpaid balance hereof at the rate provided for in this Note 
until the entire balance has been paid in full, notwithstanding the entry of any
judgement against Borrower.

PREPAYMENT - If this Note bears interest at a floating or variable rate and no 
floor or minimum rate is specified, Borrower may repay all or any portion of the
principal balance of this Note at any time, without premium or penalty. If not 
permitted under the preceding sentence, any prepayment of principal (including 
any principal repayment as a result of acceleration by Bank of this Note) shall 
require immediate payment to Bank of a prepayment fee equal to the amount, if 
any, by which the aggregate present value of schedule principal and interest 
payments eliminated by the prepayment exceeds the principal amount being 
prepaid. Said present value shall be calculated by application of a discount 
rate determined by Bank in its reasonable judgement to be the yield-to-maturity 
at the time of prepayment on U.S. Treasury securities having a maturity which 
most closely approximates the final maturity date of the principal balance then 
outstanding. Whether or not a prepayment fee is required hereunder, prepayments 
shall be applied to scheduled installments of principal in the inverse order of 
their maturity, shall be accompanied by payment of accrued interest on the 
principal amount being prepaid and, unless this Note has been accelerated by 
Bank, shall not be permitted in an amount less than the scheduled principal 
installment immediately prior to final maturity of the outstanding principal 
balance.

COLLATERAL - As security for all indebtedness to Bank now or hereafter incurred 
by Borrower, under this Note or otherwise, Borrower grants Bank a lien upon and 
security interest in any securities, instruments or other personal property of
Borrower now or hereafter in Bank's possession and in any deposit balances now 
or hereafter held by Bank for Borrower's account, and in all proceeds of any 
such personal property or deposit balances. Such liens and security interest 
shall be independent of Bank's right of setoff. This Note and the indebtedness 
evidenced hereby shall be additionally secured by any lien or security interest 
evidenced by a writing (whether now existing or hereafter executed) which 
contains a provision to the effect that such lien or security interest is 
intended to secure (a) this Note or the indebtedness evidenced hereby or (b) any
category of liabilities, obligations or indebtedness of Borrower to Bank which 
includes this Note or the indebtedness evidenced hereby, and all property 
subject to any such lien or security interest shall be collateral for this Note.

EVENTS OF DEFAULT - Each of the following shall be an Event of Default
hereunder: (a) the nonpayment when due of any amount payable under this Note or
under any obligation or indebtedness to Bank of Borrower or any person liable,
either absolutely or contingently, for payment of any indebtedness evidenced
hereby, including endorsers, guarantors and sureties (each such person is
referred to as an "Obligor"); (b) if Borrower or any Obligor has failed to
observe or perform any other existing or future agreement with Bank of any
nature whatsoever; (c) if any representation, warranty, certificate, financial
statement or other information made or given by Borrower or any Obligor to Bank
is materially incorrect or misleading; (d) if Borrower or any Obligor shall
become insolvent or make an assignment for the benefit of creditors or if any
petition shall be filed by or against Borrower or any Obligor under any
bankruptcy or insolvency law; (e) the entry of any judgement against Borrower or
any Obligor which remains unsatisfied for 15 days or the issuance of any
attachment, tax lien, levy or garnishment against any property of material value
in which Borrower or any Obligor has an interest; (f) if any attachment, levy,
garnishment or similar legal process is served upon Bank as a result of any
claim against Borrower or any Obligor or against any property of Borrower or any
Obligor; (g) the dissolution, merger, consolidation, or the sale or change in
control (as control is defined in Rule 12b-2 under the Securities Exchange Act
of 1934) of any Borrower which is a corporation or partnership, or transfer of
any substantial portion of any of Borrower's assets, or if any agreement for
such dissolution, merger, consolidation, change in control, sale or transfer is
entered into by Borrower, without the written consent of Bank; (h) the death of
any Borrower or Obligor who is a natural person; (i) if Bank determines
reasonably and in good faith that an event has occurred or a condition exists
which has had, or is likely to have, a material adverse effect on the financial
condition or creditworthiness of Borrower or any Obligor, or on the ability of
Borrower or any Obligor to perform its obligation evidenced by this Note; (j) if
Borrower shall fail to remit promptly when due to the appropriate government
agency or authorized depository, any amount collected or withheld from any
employee of Borrower for payroll taxes, Social Security payments or similar
payroll deductions; (k) if any Obligor shall attempt to terminate or disclaim
such Obligor's liability for the indebtedness evidenced by this Note; (l) if
Bank shall reasonably and in good faith determine and notify Borrower that any
collateral for this Note or for the indebtedness evidenced hereby is
insufficient as to quality or quantity; (m) if Borrower shall fail to pay when
due any material indebtedness for borrowed money other than to Bank; or (n) if
Borrower shall be notified of the failure of Borrower or any Obligor to provide
such financial and other information promptly when reasonably requested by Bank.
If this Note is payable on demand, Bank's right to demand payment hereof shall
not be restricted or impaired by the absence, non-occurrence or waiver of an
Event of Default, and it is understood that if this Note is payable on demand,
Bank may demand payment at any time.

BANK'S REMEDIES - Upon the occurrence of one or more Events of Default
(including, if this Note is payable on demand, any Event of Default resulting
from Borrower's failure to make any payment hereunder when demanded), unless
Bank elects otherwise, the entire unpaid balance of this Note and all accrued
interest shall be immediately due and payable without notice to Borrower or any
Obligor, and Bank may, immediately or at any time thereafter, exercise any or
all of its rights and remedies hereunder or under any agreement or otherwise
under applicable law against Borrower, any Obligor and any collateral. Bank may
exercise it rights and remedies in any order and may, at its option, delay in or
refrain from exercising some or all of its rights and remedies without prejudice
thereto. Upon the occurrence of any such Event of Default or at any time
thereafter, Bank may, at its option, and upon five days' written notice to
Borrower, begin accruing interest on this Note, at a rate not to exceed five
percent (5%) per annum in excess of the greater of (a) the rate of interest
provided for above, or (b) the Prime Rate in effect from time to time on the
unpaid principal balance hereof:


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* CoreStates Bank, N.A. also conducts business as Philadelphia National Bank, as
  CoreStates First Pennsylvania Bank and as CoreStates Hamilton Bank.

<PAGE>
 
provided, however, that no interest shall accrue hereunder in excess of the 
maximum rate permitted by law. All such additional interest shall be payable on 
demand.

CONFESSION OF JUDGEMENT -  Borrower irrevocably authorizes and empowers any 
attorney or any clerk of any court of record, to appear for and confess 
judgement against Borrower for such sums as are due and owing on this Note, with
or without declaration, with costs of suit, without stay of execution and with 
an amount not to exceed the greater of fifteen percent (15%) of the principal 
amount of such judgement or $5,000 added for collection fees. If a copy of this 
Note, verified by affidavit by or on behalf of Bank, shall have been filed in 
such action, it shall not be necessary to file the original of this Note. The 
authority granted hereby shall not be exhausted by the initial exercise thereof 
and may be exercised by Bank from time to time. There shall be excluded from the
lien of any judgement obtained solely pursuant to the paragraph all improved
real estate in any area identified as having special flood hazards under
regulations promulgated under the Flood Disaster Protection Act of 1973, if the
community in which such area is located is participating in the National Flood
Insurance Program. Any such exclusion shall not affect any lien upon property
not so excluded.

NOTICE TO BORROWER - Any notice required to be given by Bank under the 
provisions of this Note shall be effective as to each Borrower and each Obligor 
when addressed to Borrower and deposited in the mail, postage prepaid, for 
delivery by first class mail at Borrower's mailing address as it appears on 
Bank's records.

DISBURSEMENT AND PAYMENTS - The proceeds of this Note, or any portion thereof,
may be credited by Bank to the deposit account of Borrower, or disbursed in any
other manner requested by Borrower and approved by Bank. If Borrower so
requests, Bank may, at its option, disburse the proceeds of this Note in more
than one disbursement on the same or different dates, but except as otherwise
agreed by Bank in writing, no action taken by Bank in response to any such
request shall be deemed to create or shall imply the existence of any commitment
or obligation to pay or credit the undisbursed portion of this Note. All
payments due under this Note are to be made in immediately available funds. If
Bank accepts payment in any other form, such payment shall not be deemed to have
been made until the funds comprising such payment have actually been received by
or made available to Bank. If Borrower is not an individual, Borrower authorizes
Bank (but Bank shall have no obligation) to charge any deposit account in
Borrower's name for any and all payments of principal, interest, or any other
amounts due under this Note.

PAYMENT OF COSTS - In addition to the principal and interest payable hereunder, 
Borrower agrees to pay Bank, on demand, all costs and expenses (including 
reasonable attorneys' fees and disbursements) which may be incurred by Bank in 
the collection of this Note or the enforcement of Bank's rights and remedies 
hereunder.

REPRESENTATIONS BY BORROWER - If Borrower is a corporation or a general or
limited partnership, Borrower represents and warrants that it is validly
existing and in good standing in the jurisdiction under whose laws it was
organized. If Borrower is a corporation, Borrower represents and warrants that
the execution, delivery and performance of this Note are within Borrower's
corporate powers, have been duly authorized by all necessary action by
Borrower's Board of Directors, and are not in contravention of the terms of
Borrower's charter, by-laws, or any resolution of its Board of Directors. If
Borrower is a general or limited partnership, Borrower represents and warrants
that the execution, delivery and performance of this Note have been duly
authorized and are not in conflict with any provision of Borrower's partnership
agreement or certificate of limited partnership. Borrower further represents and
warrants that this Note has been validly executed and is enforceable in
accordance with its terms, that the execution, delivery and performance by
Borrower of this Note are not in contravention of law and do not conflict with
any indenture, agreement or undertaking to which Borrower is a party or is
otherwise bound, and that no consent or approval of any governmental authority
or any third party is required in connection with the execution, delivery and
performance of this Note.

WAIVERS, ETC. - Borrower and each Obligor waive presentment, dishonor, notice of
dishonor, protest and notice of protest. Neither the failure nor any delay on
the part of Bank to exercise any right, remedy, power or privilege hereunder
shall operate as a waiver or modification thereof. No consent, waiver or
modification of the terms of this Note shall be effective unless set forth in a
writing signed by Bank. All rights and remedies of Bank are cumulative and
concurrent and no single or partial exercise of any power or privilege shall
preclude any other or further exercise of any right, power or privilege.

MISCELLANEOUS - This Note is the unconditional obligation of Borrower, and 
Borrower agrees that Bank shall not be required to exercise any of its rights or
remedies against any collateral in which it holds a lien or security interest or
against which it has a right of setoff or against any particular Obligor. All 
representations, warranties and agreements herein are made jointly and severally
by each Borrower. If any provision of this Note shall be held invalid or
unenforceable, such invalidity or unenforceability shall not affect any other
provision hereof. To the extent that this Note represents a replacement,
substitution, renewal or refinancing of a pre-existing note or other evidence of
indebtedness, the indebtedness represented by such preexisting note or other
instrument shall not be deemed to have been extinguished hereby. In the event
that any due date specified or otherwise provided for in this Note shall fall on
a day on which Bank is not open for business, such due date shall be postponed
until the next banking day, and interest and any fees or similar charges shall
continue to accrue during such period of postponement. This Note has been
delivered in and shall be governed by and construed in accordance with the laws
of the Commonwealth of Pennsylvania without regard to the law of conflicts. This
Note shall be binding upon each Borrower and each Obligor and upon their
personal representatives, heirs, successors and assigns, and shall benefit Bank
and its successors and assigns.

CONSENT TO JURISDICTION AND VENUE -- IN ANY LEGAL PROCEEDING INVOLVING, 
DIRECTLY OR INDIRECTLY, ANY MATTER ARISING OUT OF OR RELATED TO THIS NOTE OR 
THE RELATIONSHIP EVIDENCED HEREBY, EACH UNDERSIGNED PARTY HEREBY IRREVOCABLY 
SUBMITS TO THE NONEXCLUSIVE JURISDICTION OF ANY STATE OR FEDERAL COURT LOCATED 
IN ANY COUNTY IN THE COMMONWEALTH OF PENNSYLVANIA WHERE BANK MAINTAINS AN 
OFFICE AND AGREES NOT TO RAISE ANY OBJECTION TO SUCH JURISDICTION OR TO THE 
LAYING OR MAINTAINING OF THE VENUE OF ANY SUCH PROCEEDING IN SUCH COUNTY. EACH 
UNDERSIGNED PARTY AGREES THAT SERVICE OF PROCESS IN ANY SUCH PROCEEDING MAY BE 
DULY EFFECTED UPON IT BY MAILING A COPY THEREOF, BY REGISTERED MAIL, POSTAGE 
PREPAID, TO EACH UNDERSIGNED PARTY.

WAIVERS OF JURY TRIAL -- EACH UNDERSIGNED PARTY HEREBY WAIVES, AND BANK BY ITS 
ACCEPTANCE HEREOF THEREBY WAIVES, TRIAL BY JURY IN ANY LEGAL PROCEEDING 
INVOLVING, DIRECTLY OR INDIRECTLY, ANY MATTER (WHETHER SOUNDING IN TORT, 
CONTRACT OR OTHERWISE) IN ANY WAY ARISING OUT OF OR RELATED TO THIS NOTE OR THE 
RELATIONSHIP EVIDENCE HEREBY. THIS PROVISION IS A MATERIAL INDUCEMENT FOR BANK 
TO ENTER INTO, ACCEPT OR RELY UPON THIS NOTE.

IN WITNESS WHEREOF, Borrower intending this to be a sealed instrument and 
intending to be legally bound hereby, has executed and delivered this Note as of
the day and year first above written.


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Name of Corporation
or Partnership        CFM Technologies, Inc.
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By:                                      By: /s/ Christopher F. McConnell
------------------------------------        ------------------------------------
  (Signature of Authorized Signer)            (Signature of Authorized Signer)

/s/ CFM                                     Christopher F. McConnell, Chairman
------------------------------------        ------------------------------------
  (Print or Type Name and Title               (Print or Type Name and Title
   of Signer Above)                            of Signer Above)


                            INDIVIDUALS SIGN BELOW


------------------------------------        ------------------------------(Seal)
(Signature of Witness)                      (Signature of Individual 
                                             Borrower)


------------------------------------        ------------------------------      
(Print or Type Name of Above                (Print of Type Name of 
 Witness)                                    Borrower Signing Above)


------------------------------------        ------------------------------(Seal)
(Signature of Witness)                      (Signature of Individual 
                                             Borrower)


------------------------------------        ------------------------------      
(Print or Type Name of Above                (Print of Type Name of 
 Witness)                                    Borrower Signing Above)