UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13D Under the Securities Exchange Act of 1934 (Amendment No. 3) NATCO GROUP INC. (NTG) (Name of Issuer) Common Stock (Title of Class of Securities) 0001057693 (CUSIP Number) David Nierenberg The D3 Family Funds 19605 NE 8th Street Camas, WA 98607 (360) 604-8600 With a copy to: Henry Lesser, Esq. DLA Piper Rudnick Gray Cary US LLP 2000 University Avenue East Palo Alto, CA 94303 (650) 833-2000 (Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications) March 25, 2008 (Date of Event which Requires Filing of this Statement) If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D and is filing this schedule because of ss.ss. 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box |_|. -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON The D3 Family Fund, L.P. -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS* WC -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Washington -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 251,249 Common shares (1.3%) ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 0 OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 251,249 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 0 -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON For the reporting person listed on this page, 251,249; for all reporting persons as a group, 1,270,388 shares (6.4%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES* |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.4% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON* PN -------------------------------------------------------------------------------- *SEE INSTRUCTIONS BEFORE FILLING OUT! 2 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON The D3 Family Bulldog Fund, L.P. -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS* WC -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Washington -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 740,294 common shares (3.7%) ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 0 OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 740,294 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 0 -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON For the reporting person listed on this page, 740,294; for all reporting persons as a group, 1,270,388 shares (6.4%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES* |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.4% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON* PN -------------------------------------------------------------------------------- *SEE INSTRUCTIONS BEFORE FILLING OUT! 3 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON The DIII Offshore Fund, L.P. -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS* WC -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Bahamas -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 278,795 common shares (1.4%) ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 0 OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 278,795 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 0 -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON For the reporting person listed on this page, 278,795; for all reporting persons as a group, 1,270,388 (6.4%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES* |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.4% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON* PN -------------------------------------------------------------------------------- *SEE INSTRUCTIONS BEFORE FILLING OUT! 4 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON Nierenberg Investment Management Company, Inc. -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS* AF -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Washington -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 0 ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 1,270,388 shares (6.4%) OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 0 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 1,270,388 shares -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON For the reporting person listed on this page, 1,270,388; for all reporting persons as a group, 1,270,388 shares (6.4%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES* |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.4% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON* CO -------------------------------------------------------------------------------- *SEE INSTRUCTIONS BEFORE FILLING OUT! 5 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON Nierenberg Investment Management Offshore, Inc. -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS* AF -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Bahamas -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 0 ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 278,795 common shares (1.4%) OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 0 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 278,795 common shares -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON For the reporting person listed on this page, 278,795; for all reporting persons as a group, 1,270,388 shares (6.4%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES* |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.4% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON* CO -------------------------------------------------------------------------------- *SEE INSTRUCTIONS BEFORE FILLING OUT! 6 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSON David Nierenberg -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) |X| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 SOURCE OF FUNDS* AF -------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e) |_| -------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Washington -------------------------------------------------------------------------------- 7 SOLE VOTING POWER 0 ----------------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY 1,270,388 common shares (6.4%) OWNED BY ----------------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON 0 WITH ----------------------------------------------------------------- 10 SHARED DISPOSITIVE POWER 1,270,388 -------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON For the reporting person listed on this page, 1,270,388; for all reporting persons as a group, 1,270,388 shares (6.4%) -------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES* |_| -------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.4% -------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON* IN -------------------------------------------------------------------------------- *SEE INSTRUCTIONS BEFORE FILLING OUT! 7 This Amendment No. 3 to Schedule 13D (this "Amendment") amends the below-indicated items from the Schedule 13D previously filed by or on behalf of the undersigned parties (the "Reporting Persons"), as previously amended (the "Schedule 13D"), by supplementing such Items with the information below: Item 2. Identity and Background. David Nierenberg is hereby added as a Reporting Person; his business address is 19605 NE 8th Street, Camas WA 98607; his principal occupation is President of Nierenberg Investment Management Company, Inc. and Nierenberg Investment Management Offshore, Inc, two of the other Reporting Persons; during the past five years he has not been convicted in a criminal proceeding required to be reported in response to Item 2(d), or a party to a civil proceeding required to be reported in response to Item 2(e), of Schedule 13D; and he is a citizen of the United States of America. Item 3. Source and Amount of Funds or Other Consideration. On March 25, 2008 the Reporting Persons acquired a total of 1,270,388 shares of NTG's common stock through conversion, in accordance with their terms and without the payment of additional consideration, all of the shares of NTG convertible preferred stock acquired by the Reporting Persons on April 7, 2006, as previously reported, that they beneficially owned immediately prior to conversion. Item 4. Purpose of the Transaction. Reference is made to the responses to Items 3 and 5, which are incorporated herein by reference. The Reporting Persons hold their shares of NTG common stock for investment. The Reporting Persons reserve the right to increase or decrease their investment in NTG depending on market conditions, circumstances affecting NTG and/or extrinsic factors such as developments in NTG' s industry and the economic environment, and to discuss NTG and their investment in the shares of NTG with the directors and executive officers of NTG and third parties, without amending the Schedule 13D except as required by applicable rules. Item 5. Interest in Securities of the Issuer. (a,b) The Reporting Persons, in the aggregate, beneficially own 1,270,388 common shares, constituting approximately 6.4% of the outstanding Shares. The Reporting Persons have determined their current individual and aggregate percentages for purposes of this Amendment based on the sum of the number of shares of NTG common stock reported to be outstanding on March 11 in NTG's Annual Report on Form 10-K for the year ended December 31, 2007 plus the number of shares of NTG common stock acquired by the Reporting Persons through conversion of convertible preferred stock (see Item 3). 8 c) On March 25, 2008, the Reporting Persons acquired the following shares of NTG common stock through conversion of convertible preferred stock (see Item 3): Transaction Common Shares Preferred Shares Portfolio Name Date Acquired Converted -------------- ----------- ------------- ---------------- D3 Family Fund LP 3/25/2008 251,249 1,961 D3 Family Bulldog Fund LP 3/25/2008 740,294 5,778 DIII Offshore Fund LP 3/25/2008 278,795 2,176 Item 7. Material to be filed as Exhibits Exhibit 1 to this Schedule 13D is the Joint Filing Agreement among the Reporting Persons dated March 5, 2008 pursuant to which all of the Reporting Persons (and one of their affiliates that owns no NTG shares and is therefore not a Reporting Person) have authorized the filing of Schedule 13D's and amendments thereto as a group. 9 SIGNATURE After reasonable inquiry and to the best of my knowledge and belief, each of the undersigned certifies that the information set forth in the Statement is true, complete and correct. D3 Family Fund, L.P., D3 Family Bulldog Fund, L.P., and D3 Family Canadian Fund, L.P. By: Nierenberg Investment Management Company, Inc. Its: General Partner March 26, 2008 By: /s/ David Nierenberg ------------------------- --------------------------------------------- David Nierenberg, President DIII Offshore Fund, L.P. By: Nierenberg Investment Management Offshore, Inc. Its: General Partner March 26, 2008 By: /s/ David Nierenberg ------------------------- --------------------------------------------- David Nierenberg, President Nierenberg Investment Management Company, Inc. March 26, 2008 By: /s/ David Nierenberg ------------------------- --------------------------------------------- David Nierenberg, President Nierenberg Investment Management Offshore, Inc. March 26, 2008 By: /s/David Nierenberg ------------------------- ------------------------------------------- David Nierenberg, President March 26, 2008 /s/ David Nierenberg -------------------------- --------------------------------------------- David Nierenberg 10