EXHIBIT 3.50

                                     BY-LAWS

                                       OF

                      PRESSURE SYSTEMS INTERNATIONAL, INC.

ARTICLE I. Stockholders.

1.       Annual Meeting. The annual meeting of stockholders commencing in 1982
shall be held in November at such time and place as is stated in the notice of
the meeting in each year (or if that be a legal holiday in the place where the
meeting is to be held, on the next succeeding full business day) fixed by the
Directors or the President and stated in the notice of the meeting. The purposes
for which the annual meeting is to be held, in addition to those prescribed by
law, by the Articles of Incorporation, or by these By-Laws, may be specified by
the Directors or the President. If no annual meeting is held in accordance with
the foregoing provisions, a special meeting may be held in lieu thereof, and any
action taken at such meeting shall have the same effect as if taken at the
annual meeting.

2.       Special Meetings. Special meetings of stockholders of the corporation
may be called at any time by the President or the Directors. It shall be the
duty of the Secretary, or in the case of the death, absence, incapacity or
refusal of the Secretary, or any other officer, to call a special meeting of the
stockholders, whenever requested in writing so to do by one or more stockholders
of record, holding at least one-tenth of the outstanding common stock of the
corporation entitled to vote, stating the time, place and purpose of the
meeting.

3.       Place of Meetings. All meetings of stockholders shall be held at the
principal office of the corporation unless a different place (within the United
States) is fixed by the Directors or the President and stated in the notice of
the meeting.

4.       Notice of Meetings. A written notice of every meeting of stockholders,
stating the place, date and hour thereof, and the purposes for which the meeting
is to be held, shall be given by the Secretary or by the person calling the
meeting at least ten days before the meeting to each stockholder entitled to
vote thereat and to each stockholder who by law, by the Articles of
Incorporation or by these By-Laws, is entitled to such notice, by leaving such
notice with him or at his residence or usual place of business, or by mailing it
postage prepaid and addressed to such stockholder at his address as it appears
upon the books of the corporation. No notice need be given to any stockholder if
a written waiver of notice, executed before or after the



meeting by the stockholder or his attorney thereunto authorized is filed with
the records of the meeting.

5.       Quorum. The holders (or their proxies) of a majority in interest of all
stock issued, outstanding and entitled to vote at a meeting shall constitute a
quorum but a lesser number may adjourn any meeting from time to time without
further notice; except that if two or more classes of stock are outstanding and
entitled to vote as separate classes, then in the case of each such class a
quorum shall consist of the holders of a majority in interest of the stock of
that class issued, outstanding and entitled to vote.

6.       Voting and Proxies. Each stockholder shall have one vote for each share
of stock entitled to vote held by him of record according to the records of the
corporation unless otherwise provided by the Articles of Incorporation.
Stockholders may vote either in person or by written proxy dated not more than
six months before the meeting named therein. Proxies shall be filed with the
Secretary of the meeting, or of any adjournment thereof, before being voted.
Except as otherwise limited therein, proxies shall entitle the persons named
thereto to vote at any adjournment of such meeting but shall not be valid after
final adjournment of such meeting. A proxy with respect to stock held in the
name of two or more persons shall be valid if executed by one of them unless at
or prior to exercise of the proxy the corporation receives a specific written
notice to the contrary from any one of them. A proxy purporting to be executed
by or on behalf of a stockholder shall be deemed valid unless challenged at or
prior to its exercise.

7.       Action at Meeting. When a quorum is present, the holders of a majority
of the stock present or represented and voting on a matter (or if there are two
or more classes of stock entitled to vote as separate classes, then in the case
of each such class, the holders of a majority of the stock of that class present
or represented and voting on a matter) except where a larger vote is required by
law, the Articles of Incorporation or these By-Laws, shall decide any matter to
be voted on by the stockholders. Any election by stockholders shall be
determined by a plurality of the votes cast by the stockholders entitled to vote
at the election. No ballot shall be required for such election unless requested
by a stockholder present or represented at the meeting and entitled to vote in
the election. The corporation shall not directly or indirectly vote any share of
its stock.

8.       Action Without Meeting. Any action to be taken by stockholders may be
taken without a meeting if all stockholders

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entitled to vote on the matter consent to the action by a writing filed with the
records of the meetings of stockholders. Such consent shall be treated for all
purposes as a vote at a meeting.

ARTICLE II. Directors.

1.       Powers. The business of the corporation shall be managed by a Board of
Directors who may exercise all the powers of the corporation except as otherwise
provided by law, by the Articles of Incorporation or by these By-Laws. In the
event of any vacancy in the Board of Directors, the remaining Directors, except
as otherwise provided by law, may exercise the powers of the full Board until
such vacancy is filled. The Board of Directors shall fix the compensation and
duties of all officers of the corporation and shall have discretionary power to
determine what constitutes net earnings, profits and surplus, respectively, what
amount shall be reserved for working capital and for any other purposes and what
amount shall be declared as dividends, and such determination by the Board of
Directors shall be final and conclusive.

2.       Election. A Board of Directors of such number as shall be fixed by the
stockholders shall be elected by the stockholders at the annual meeting.

3.       Enlargement of the Board. The number of the Board of Directors may be
increased and one or more additional Directors elected at any special meeting of
the stockholders or by the Directors by vote of a majority of the Directors then
in office, provided the Directors may not increase the number of Directors to
more than six.

4.       Vacancies. Any vacancy in the Board of Directors, including a vacancy
resulting from the enlargement of the Board, may be filled by the stockholders
or by the Directors. Any person who may have been chosen by the Directors to
fill such vacancy shall be displaced by a different person if chosen by the
stockholders to fill such vacancy.

5.       Tenure. Except as otherwise provided by law, by the Articles of
Incorporation, or by these By-Laws, Directors shall hold office until the next
annual meeting of stockholders and thereafter until their successors are chosen
and qualified. Any Director may resign by delivering his written resignation to
the corporation at its principal office or to the President or Secretary.

Such resignation shall be effective upon receipt unless it is specified to be
effective at some other time or upon the happening of some other event.

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6.       Removal. A Director may be removed from office (a) with or without
cause by vote of a majority of the stockholders entitled to vote in the election
of Directors, provided that the Directors of a class elected by a particular
class of stockholders may be removed only by the vote of the holders of a
majority of the shares of such class, or (b) for cause by vote of a majority of
the Directors then in office. A Director may be removed for cause only after
reasonable notice and opportunity to be heard before the body proposing to
remove him.

7.       Meetings. Regular meetings of the Directors may be held without call or
notice at such places within or without Virginia and at such times as the
Directors may from time to time determine, provided that any Director who is
absent when such determination is made shall be given notice of the
determination. Such notice shall be sufficient if mailed by the Secretary, or
Assistant Secretary, postage prepaid, to such Director at his business or home
address. A regular meeting of the Directors may be held without a call or notice
at the same place as the annual meeting of stockholders, or the special meeting
held in lieu thereof, following such meeting of stockholders.

Special meetings of the Directors may be held at any time and place designated
in a call by the President, Treasurer or a majority of the Directors then in
office.

The Chairman of the Board of Directors, if there be one, shall preside at all
meetings of the Board, and in his absence, the President, or a Vice President in
the order of seniority, shall preside; otherwise, a temporary Chairman shall be
elected by the Directors to preside.

8.       Notice of Meetings. Notice of all special meetings of the Directors
shall be given to each Director by the Secretary or Assistant Secretary, or in
the case of the death, absence, incapacity or refusal of such persons, by the
officer or one of the Directors calling the meeting. Notice shall be given to
each Director in person or by telephone or by telegram sent to his business or
home address at least twenty-four hours in advance of the meeting, or by written
notice mailed to his business or home address at least forty-eight hours in
advance of the meeting. Notice need not be given to any Director if a written
waiver of notice, executed by him before or after the meeting, is filed with the
records of the meeting, or to any Director who attends the meeting without
protesting prior thereto or at its commencement the lack of notice to him. A
notice of waiver of a Directors' meeting need not specify the purposes of the
meeting.

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9.       Quorum. At any meeting of the Directors, a majority of the Directors
then in office shall constitute a quorum. Less than a quorum may adjourn any
meeting from time to time without further notice.

10.      Action at Meeting. At any meeting of the Directors at which a quorum is
present, the vote of a majority of those present on any matter, unless a
different vote is specified by law, by the Articles of Incorporation, or by
these By-Laws, shall be sufficient to decide such matter.

11.      Action by Consent. Any action by the Directors may be taken without a
meeting if a written consent thereto is signed by all the Directors and filed
with the records of the Directors' meetings. Such consent shall be treated as a
vote of the Directors for all purposes.

12.      Committees. The Directors may, by vote of a majority of the Directors
then in office, elect from their number an executive or other committee and may
by like vote delegate thereto some or all of their powers except those which by
law, the Articles of Incorporation or these By-Laws, they are prohibited from
delegating. Except as the Directors may otherwise determine, any such committee
may make rules for the conduct of its business, but unless otherwise provided by
the Directors or in such rules, its business shall be conducted as nearly as may
be in the same manner as is provided by these By-Laws for the Directors.

ARTICLE III. Officers.

1.       Enumeration. The officers of the corporation shall consist of a
President, a Treasurer, a Secretary and such other officers, including a
Chairman of the Board, one or more Vice Presidents, Assistant Secretaries and
Assistant Treasurers as the Directors may determine.

2.       Election. The President, Treasurer and Secretary shall be elected
annually by the Directors at their first meeting following the annual meeting of
stockholders or special meeting in lieu thereof. Other officers may be chosen by
the Directors at such meeting or at any other meeting.

3.       Qualification. The President may, but need not be, a Director. No
officer need be a stockholder. Any two or more offices may be held by the same
person. The Secretary shall be a resident of Virginia unless the corporation has
a resident agent appointed for the purpose of service of process. Any officer
may be required by the Directors to give bond for the faithful performance of
his duties to the corporation in

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such amount and with such sureties as the Directors may determine.

4.       Tenure. Except as otherwise provided by law, the Articles of
Incorporation, or by these By-Laws, the President, Treasurer and Secretary shall
each hold office until the first meeting of the Directors following the annual
meeting of stockholders and thereafter until his successor is chosen and
qualified; and all other officers shall each hold office until removed by the
Directors, or until his successor is chosen and qualified unless a shorter term
is specified in the vote choosing or appointing him. Any officer may resign by
delivering his written resignation to the corporation at its principal office or
to the President or Secretary, and such resignation shall be effective upon
receipt unless it is specified to be effective at some other time or upon the
happening of some other event.

5.       Removal. The Directors may remove any officer with or without cause by
a vote of a majority of the Directors then in office, provided that an officer
may be removed for cause only after reasonable notice and opportunity to be
heard by the Board of Directors prior to action thereon.

6.       President and Vice Presidents. The President shall be the chief
executive officer of the corporation and shall, subject to the direction of the
Directors, have general supervision and control of its business. Unless
otherwise provided by the Directors, he shall preside, when present, at all
meetings of the stockholders and in the absence of a Chairman of the Board of
Directors at all meetings of the Directors.

Any Vice President shall have such powers as the Directors may from time to time
designate.

7.       Treasurer and Assistant Treasurers. The Treasurer shall, subject to the
direction of the Directors, have general charge of the financial affairs of the
corporation. He shall have custody of all funds, securities and valuable
documents of the corporation, except as the Directors may otherwise provide. He
may endorse for deposit or collection all checks, notes, etc. payable to the
corporation or its order and may accept drafts on behalf of the corporation. He
shall cause to be kept accurate accounts of the corporation's transactions. The
Board of Directors shall determine the individuals who will be authorized to
sign on the corporation's bank account.

Any Assistant Treasurer shall have such powers as the Directors may from time to
time designate.

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8.       Secretary and Assistant Secretaries. The Secretary shall keep a record
of the meetings of stockholders and directors. Unless a Transfer Agent is
appointed, the Secretary shall keep or cause to be kept in Virginia, at the
principal office of the corporation, or at his office, the stock and transfer
records of the corporation in which are contained the names of all stockholders
and the record address and the amount of stock held by each.

In the absence of the Secretary from any meeting of stockholders or Directors,
an Assistant Secretary, if one be chosen, otherwise a Temporary Secretary
designated by the person presiding at the meeting, shall perform the duties of
the Secretary,

9.       Other Powers and Duties. Each office shall, subject to these By-Laws,
have in addition to the duties and powers specifically set forth in these
By-Laws, such other duties and powers as the Directors may from time to time
designate.

10.      Indemnification. Each person now or hereafter a Director or officer of
the corporation, or who serves at its request as a Director or officer of any
other corporation in which it has an interest, shall be indemnified by this
corporation to the fullest extent as may be allowed by the laws of the
Commonwealth of Virginia.

ARTICLE IV. Common Stock.

1.       Certificates of Stock. Each stockholder shall be entitled to a
certificate of the common stock of the corporation held by him in such form as
may be prescribed from time to time by the Directors. The certificate shall be
signed by the President or a Vice President and by the Secretary or an Assistant
Secretary, but when a certificate is countersigned by a transfer agent or a
registrar, other than a Director, officer or employee of the corporation, such
signatures may be facsimiles. In case any officer who has signed or whose
facsimile signature has been placed on such certificate shall have ceased to be
such officer before such certificate is issued, it may be issued by the
corporation with the same effect as if he were such officer at the time of its
issue.

2.       Transfers. Subject to the restrictions, if any, on the transfer of
stock, shares of stock may be transferred on the books of the corporation by the
surrender to the corporation or its transfer agent of the certificate therefor
properly endorsed or accompanied by a written assignment and power of attorney
properly executed, and with such proof of the authenticity of signature as the
corporation or its transfer agent may reasonably require. Except as may be
otherwise

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required by law, by the Articles of Incorporation, or by these By-Laws, the
corporation shall be entitled to treat the record holder of stock as shown on
its books as the owner of such stock for all purposes, including the payment of
dividends and the right to vote with respect thereto, regardless of any
equitable or other claim thereto, on the part of any other person, until the
shares have been transferred on the books of the corporation in accordance with
the requirements of these By-Laws.

It shall be the duty of each stockholder to notify the corporation of his post
office address.

3.       Record Date. The Directors may fix in advance a time of not more than
sixty days preceding the date of any meeting of the stockholders, or the date
for the payment of any dividend, or the making of any distribution to
stockholders, or the last day on which the consent or dissent of stockholders
may be effectively expressed for any purpose, as the record date for determining
the stockholders having the right to notice of and to vote at such meeting, and
any adjournment thereof, or the right to receive such dividend or distribution,
or the right to give such consent or dissent. In such case only stockholders of
record on such record date shall have such right, notwithstanding any transfer
of stock on the books of the corporation after the record date. Without fixing
such record date, the Directors may, for any of such purposes, close the
transfer books for all or any part of such period.

4.       Replacement of Certificates. In case of the alleged loss or destruction
or the mutilation of a certificate of stock, a duplicate certificate may be
issued in place thereof, upon such terms as the Directors may prescribe.

ARTICLE V. Miscellaneous Provisions.

1.       Fiscal Year. Except as from time to time otherwise determined by the
Directors, the fiscal year of the corporation shall be the twelve months ending
the last day of October.

2.       Seal. The seal of the corporation shall, subject to alteration by the
Directors, bear its name, the word "Virginia" and the year of incorporation.

3.       Execution of Instruments. All deeds, leases, transfers, contracts,
bonds, notes and other obligations authorized to be executed by an officer of
the corporation in its behalf shall be signed by the President or the Secretary,
except as the Directors may generally or in particular cases otherwise
determine.

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4.       Voting of Securities. Except as the Directors may otherwise designate,
the President or Treasurer may waive notice of, and appoint any person or
persons to act as proxy or attorney in fact for this corporation (with or
without power of substitution) at, any meeting of stockholders or shareholders
of any other corporation or organization, the securities of which may be held by
this corporation.

5.       Corporate Records. The original, or attested copies, of the Articles of
Incorporation, By-Laws and records of all meetings of the incorporators and
stockholders, and the stock and transfer records, which shall contain the names
of all stockholders and the record address and the amount of stock held by each,
shall be kept in Virginia at the principal office of the corporation, or at an
office of its transfer agent or of the Secretary. Said copies and records need
not all be kept in the same office.

6.       Articles of Incorporation. All references in these By-Laws to the
Articles of Incorporation shall be deemed to refer to the Articles of
Incorporation of the corporation as amended and in effect from time to time.

7.       Amendments. These By-Laws may at any time be amended by vote of the
stockholders, provided that notice of the substance of the proposed amendment is
stated in the notice of the meeting, or may be amended by vote of a majority of
the Directors then in office, except that no amendment may be made by the
Directors which changes the date of the annual meeting of stockholders, or which
alters the provisions of these By-Laws with respect to removal of Directors or
the election of committees by Directors and delegation of powers thereto, the
enlargement of the Board of Directors and the election of Directors to fill
vacancies, or the amendment of these By-Laws. No change in the date of the
annual meeting may be made within sixty days before the date fixed in these
By-Laws. Not later than the time of giving notice of the meeting of stockholders
next following the making, amending or repealing by the Directors of any By-Law,
notice thereof stating the substance of such change shall be given to all
stockholders entitled to vote on amending the By-Laws.

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