Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
OMB APPROVAL
OMB Number: 3235-0287
Expires: January 31, 2005
Estimated average burden hours per response... 0.5

(Print or Type Responses)
1. Name and Address of Reporting Person *
LIME ROCK PARTNERS II LP
   2. Issuer Name and Ticker or Trading Symbol
NATCO GROUP INC [NTG] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
(Last)
(First)
(Middle)
C/O LIME ROCK MANAGEMENT LP, 518 RIVERSIDE AVENUE		 3. Date of Earliest Transaction (Month/Day/Year)
04/07/2006
(Street)

WESTPORT, CT 06880		 4. If Amendment, Date Original Filed(Month/Day/Year)
 6. Individual or Joint/Group Filing(Check Applicable Line)
___ Form filed by One Reporting Person
_X_ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)		 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)		 4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)		 5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)		 6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)		 7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
Common Stock (1) 04/07/2006   S   110,061 D $ 25.29 0 D (2)  

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number. SEC 1474 (9-02)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)		 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)		 5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)		 6. Date Exercisable and Expiration Date
(Month/Day/Year)		 7. Title and Amount of Underlying Securities
(Instr. 3 and 4)		 8. Price of Derivative Security
(Instr. 5)		 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)		 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)		 11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Series B Convertible Preferred Stock $ 7.805 (3) 04/07/2006   S     15,000   (4)   (4) Common Stock 1,921,844 $ 3,453.473 0 D (2)  

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
LIME ROCK PARTNERS II LP
C/O LIME ROCK MANAGEMENT LP
518 RIVERSIDE AVENUE
WESTPORT, CT 06880		     X    
Lime Rock Partners GP II, L.P.
C/O LIME ROCK MANAGEMENT LP
518 RIVERSIDE AVENUE
WESTPORT, CT 06880		     X    
LRP GP II, Inc.
C/O LIME ROCK MANAGEMENT LP
518 RIVERSIDE AVENUE
WESTPORT, CT 06880		     X    

Signatures

 LIME ROCK PARTNERS II, L.P., by Lime Rock Partners GP II, L.P., its General Partner, by LRP GP II, Inc., its General Partner By: Mark A. McCall   04/11/2006
**Signature of Reporting Person Date
 LIME ROCK PARTNERS GP II, L.P., By: LRP GP II, Inc., its General Partner, By: Mark A. McCall   04/11/2006
**Signature of Reporting Person Date
 LRP GP II, INC. By: Mark A. McCall   04/11/2006
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) This Form 4 is filed by Lime Rock Partners II, L.P. ("Fund"), Lime Rock Partners GP II, L.P. ("GP LP"), and LRP GP II, Inc. ("GP Inc.").
(2) The Fund is the direct beneficial owner of Issuer's securities. GP LP may be deemed to be an indirect beneficial owner of Issuer's securities because of its position as general partner of the Fund and its entitlement to a share of the Fund's profits, and GP Inc. may be deemed to be an indirect beneficial owner of the Issuer's securities because it is the general partner of GP LP and is entitled to a share of GP LP's profits. GP LP and GP Inc. each disclaim beneficial ownership of these securities and this report shall not be deemed to be an admission that GP LP or GP Inc. is the beneficial owner of such securities.
(3) Based on a face value of $1,000 per share of the Series B Convertible Preferred Stock.
(4) The Series B convertible preferred stock is convertible into common stock of the Issuer at any time at the option of the holder and has no expiration date.

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB number.