Getting Started with TruBlu
Cautions/Safety
TruBlu hoses are intended for use by professionally trained HVAC technicians. TruBlu hoses are not
intended for pressure. They are designed for vacuum only the same as your vacuum pump. Pressurizing
a vacuum hose could cause displacement of the O-ring seal which leads to pressure loss, refrigerant loss,
and could cause bodily injury.
Always wear gloves and goggles and other required PPE when
working on or around refrigerants.
Product Use
TruBlu hoses use KF or Quick Flange fittings. KF fittings allow for one hose to be used in multiple applications
with a variety of end configurations. The hose can also be connected to a tee ‘T’ or wye ‘Y’ fitting to further
expand the system flexibility. KF fittings use a taper lock flange and clamp connection that is sealed with
an O-ring. Unlike typical KF fittings used in industrial vacuum service, TruBlu hoses have the centering ring
built into the flange to prevent the centering O-ring from falling on the ground when end changing fittings
in the field (patent pending).
Once an end fitting is installed on a hose there is no need to remove it unless you want to change the hose
configuration. Leaving the fittings on the hoses prevents damage to the O-rings and protects the flanges
from damage. A plastic cap is included with each end connection, and it is advised that end connections that
are not in use the flange is capped. This will prevent the sealing surface from getting scratched, nicked, or
marred. The flat surface is the sealing surface, and care should be taken that it is not damaged.
There are two types of clamps provided in your kit, a stainless low-profile type (p. 6 left) and a larger
aluminum clamp (p.6 right). These are standard KF style clamps. Clamp wing nuts only need to be finger
tight. The connection is actually self-sealing under vacuum. The low-profile clamp is intended to be used on
the hose end that connects to the Schrader core removal tool and intern the equipment, the larger clamps
are intended to be used where space is not limited.
KF Fitting with Integrated O-Ring
Hose-end Flange Face
5
4
The conductance speed of 1/4" OD refrigeration tubing is too small to be useful as a
connecting line in a system; so small we will not even discuss it. Never use it if you can avoid
it as it is too costly in excessive pump-down time.
Review of Vacuum for Service Engineers
,
Saunders and Williams Copyright 1959, Revised 1988, p. 60.
Mathematically it is important to understand that increasing the diameter of a hose does not have a
linear effect but rather that to a ratio of its diameter to the third or fourth power. By diameter, we’re
talking ID not OD.
Comparing 1/4" ID hose to TruBlu 3/4" ID hose shows a Conductance Speed increase of approximately
96 times faster! (.25
4
= .00331) vs. (.75
4
= .31972) or (.31972/.00331 = 96.5)
In addition to higher conductance, we need to consider the type of flow. In vacuum there are three types of
flow to consider: viscous, laminar, and molecular. Viscous flow means we have a steady stream of molecules
flowing through the pipe. As we get to laminar and molecular flow things really slow down, so staying in the
viscous flow region is critical for quick evacuation times (and hence, our focus!).
Viscous flow ends where the microns are approximately 100/d" or 100/internal diameter of the tubing in
inches. When comparing viscous flow in various diameters, again you can see that 3/4" tubing has a huge
advantage. Viscous flow stops in 1/4" tubing at 400 microns (100/.25" = 400 Microns) where 3/4" viscous flow
continues to 133 microns (100/.75" = 133 microns). This is important because with a larger diameter we get
a 3X deeper vacuum in the viscous flow region (400/133= 3.00). A deeper vacuum means faster degassing
and much better dehydration. Dehydration is critical more than ever for systems contaminated with POE oils
since moisture breaks-down the oil forming sludge and acids.
So how much faster is a 5 foot, 3/4" ID hose than 1/4" ID at 500 microns? Approximately 80 times faster.
The conductance for air at 68°F is expressed as 520 x d
4
x P/L where P is the pressure in mm Hg Absolute and
length is expressed in feet of hose.
Where 500 microns
= .5 mm Hg abs
(520 x .25"
4
x .500)/5' = .2 CFM
(520 x .75"
4
x .500)/5' = 16 CFM
16 CFM/.2 CFM
= 80 CFM faster at 500 microns of Hg
What does all this mean?
Short fat hoses trump long
skinny ones, every time!
