Internal Rod Load, Gas
Internal gas Rod Load is the force
imposed on the rod, caused by pressure inside the cylinder against the
head end and crank end piston areas. Below rod load calculations use gauge pressures. Ariel
uses cylinder internal pressures
to calculate gas rod loads.
Double Acting
Cylinders
RLc
= Ahe
x Pd
-Ace
x Ps
RLt
= Ace
x Pd -
Ahe
x Ps
For Single Acting (Crank End)
Cylinders
RLc
= Ahe
x Ps
- Ace
x Ps
RLt =
Ace
x Pd
- Ahe x
Ps
To obtain rod load reversal, it
is recommended to single act cylinders by deactivating the head end (removing
or unloading the head end suction valve(s)). Deactivating the crank end
may cause a non-reversing rod load and must be carefully evaluated.
Tandem Cylinders
Tandem Cylinders - (High Pressure
Cylinder Outboard)
RLc
= Ahe(HP)
x Pdi(HP)
+[Ahe(LP)
- Ahe(HP)]
x Psflg(LP)
- Ace(LP)
x Psi(LP)
RLt
= Ace(LP)
x Pdi(LP)
- [Ahe(LP)
- Ahe(HP)]
x Psflg(LP)
- Ahe(HP)
x Psi(HP)
High Pressure Cylinder Outboard
Tandem Cylinders - (High Pressure
Cylinder Inboard)
RLc
= Ahe(LP)
x Pdi(LP)
- [Ahe(LP)
- Ahe(HP)]
x Psflg(LP)
- Ace(HP)
x Psi(HP)
RLt
= Ace(HP)
x Pdi(HP)
+ [Ahe(LP)
- Ahe(HP)]
x Psflg(LP)
- Ahe(LP)
x Psi(LP)
High Pressure Cylinder Inboard
RLc=
Internal compression gas rod load, lbf
RLt=
Internal tension gas rod load, lbf
Ahe=
Piston head end area, in2
Ace=
Piston crank end area, in2
Ahe(hp)=
High pressure cylinder piston head end area, in2
(for tandem
cylinders)
Ace(hp)=
High pressure cylinder piston crank end area, in2
(for tandem cylinders)
Ahe(lp)=
Low pressure cylinder piston head end area, in2
(for tandem cylinders)
Ace(lp)=
Low pressure cylinder piston crank end area, in2
(for tandem cylinders)
Ps
= Internal suction
pressure, psig
Pd
= Internal discharge
pressure, psig
Ps(hp)
= High pressure cylinder
internal suction pressure, psig
Pd(hp)=
High pressure cylinder internal discharge pressure, psig
Ps(lp)=
Low pressure cylinder internal suction pressure, psig
Pd(lp)=
Low pressure cylinder internal discharge pressure, psig
Gauge pressures are used in the
above equations for simplicity. Absolute
pressure can be used for gas rod load calculations. However,
the above equations would need to be modified to include the atmospheric
pressure on the free end of the piston rod.
Ariel
Corporation Application Manual
23 Dec 2010