SUBROUTINE TYPE65 (TIME,XIN,OUT,T,DTDT,PAR,INFO,ICNTRL,*) 
C*      SUBROUTINE PRESIST (P,M,PEnt,PLvg,ErrStat)
C***********************************************************************
C*    Copyright ASHRAE.  Toolkit for HVAC System Energy Calculations
c*    Revised for TRNSYS by N.Blair and R.Schwarz
C***********************************************************************
C*    SUBROUTINE:             PRESIST
C*
C*    LANGUAGE:               FORTRAN 77
C*
C*    PURPOSE:                Calculates the pressure loss through a
C*                            flow resistance.  Outlet pressure is a
C*                            function of inlet pressure and flow rate.
C***********************************************************************
C*    INPUT VARIABLES  DESCRIPTION(UNITS)                     Sample Values
C*    XIN(1)       M Mass flow rate through valve (kg/s)           -.5
C*    XIN(2)    PEnt Pressure of fluid entering valve (Pa)         101325.0
C*
C*    OUTPUT VARIABLES
C*    OUT(1)    PLvg Pressure of fluid leaving valve (Pa)          107759.0
C*    OUT(2) ErrStat Error status indicator, 0 = ok, 1 = error (-)      0.0
C*
C*    PARAMETERS
C*    PAR(1)  Resist Flow resistance coefficient (1/kg m)           25735.0
C***********************************************************************
C     MAJOR RESTRICTIONS:     Pressure drop proportional to square of
C                             flow rate.
C
C     DEVELOPER:              Michael J. Brandemuehl, PhD, PE
C                             University of Colorado at Boulder
C
C     DATE:                   May 1, 1992
C
C     INCLUDE FILES:          presist.inc
C     SUBROUTINES CALLED:     None
C     FUNCTIONS CALLED:       None
C
C     REVISION HISTORY:       None
C
C     REFERENCE:              None
C***********************************************************************
C     INTERNAL VARIABLES:
C     deltaP        Pressure drop across the valve                  (Pa)
C***********************************************************************

	DOUBLE PRECISION XIN, OUT
      INTEGER ErrStat, INFO, IOPT, NI, NP, ND
      DIMENSION XIN(2),OUT(1),PAR(1),INFO(15)
      REAL PAR
      CHARACTER*3 YCHECK(2), OCHECK(1)

	DATA YCHECK/'MF2','PR3'/
	DATA OCHECK/'PR3'/

      ErrStat = 0
	IOPT	= -1
	NI		= 2		!CORRECT NUMBER OF INPUTS
	NP		= 1		!CORRECT NUMBER OF PARAMETERS
	ND		= 0		!CORRECT NUMBER OF DERIVATIVES

      M		=XIN(1)
      PEnt	=XIN(2)
 
      Resist	=PAR(1)
	
      IF (INFO(7).EQ.-1) THEN
		CALL TYPECK(IOPT,INFO,NI,NP,ND)
C	CHECKS TO SEE IF USER'S INFO MATCHES CORRECT NUMBERS
		CALL RCHECK(INFO,YCHECK,OCHECK)
C	CHECKS TO SEE IF INPUT AND OUTPUT UNITS MATCH
	ENDIF      

C1*** Calculate the pressure drop.
C2*** M*ABS(M) allows negative deltaP for negative M.

      deltaP = Resist*M*ABS(M)

C1*** Calculate the outlet pressure.

      PLvg = PEnt-deltaP

      OUT(1) = Plvg
      OUT(2) = ERRSTAT

      RETURN 1
      END