Overview
Modified high-pressure by-pass valve. HydraMaster part number 000-169-083, listed as Valve, Hi PSI By-Pass — Modified and, in the suggested spares schedule, as valve, mod. hi pressure bypass.
The by-pass valve is what sets solution pressure. It holds the pump's output at the set point and dumps the excess back to the water box. Almost every pressure complaint on a truckmount comes back to this valve, the pump, or a restriction — and the by-pass is the cheapest of the three to check.
What it fits
Named in the parts lists of:
- HydraMaster Boxxer 427
- HydraMaster MAXX 450D / 470D / Diesel
- HydraMaster CM402
HydraMaster's suggested spares schedule lists it against the Boxxer 421, Boxxer 427 and MAXX 450D / 470D. CCW's own record adds the MAXX 470 and covers the BX421, BX427, MX450 and MX470.
Service parts for this valve
A by-pass valve that will not hold pressure does not always need replacing. CCW stocks its wear parts:
- 169-204 — Ball, stainless steel, for by-pass valve 169-083
- 097-028 — O-ring kit (listed for by-pass valve 169-101, and worth checking against your valve)
HydraMaster also list 155-021, the red 0–1000 psi by-pass spring, for the CDS 4.8 and SpitFire 3.2. It is not currently a stocked CCW line — ask us if you need one.
How by-pass faults present
- Pressure reads correctly at rest and collapses under trigger — worn seat or ball. This is the classic by-pass symptom.
- Pressure will not reach the set point at all — could be by-pass, could be pump. Check the by-pass first; it is cheaper to rule out.
- Pressure creeps up or hunts — a ball not seating cleanly, often because of debris rather than wear.
- Cannot adjust pressure any more — spring or seat.
Debris in the seat is the most common single cause, and it usually arrives because the ¼ inch Y strainer screen upstream has been neglected. Fix the cause as well as the symptom.
Fitting advice
Note the pressure setting before you touch anything. It is far easier to return to a known figure than to find it again by trial.
Depressurise the system before you open the valve.
Check the ball and seat while it is apart — a pitted seat will not seal against a new ball, and at that point the valve is finished rather than serviceable.
Frequently asked questions
Should I repair or replace?
Try the ball and seals first unless the seat is pitted or the body is damaged. Ask us and we will help you decide.
Is this the same as 169-101?
No. 169-101 is the by-pass valve listed for the CDS 4.6/4.8 and SpitFire 3.2. This one is the modified high-pressure by-pass for the Boxxer and MAXX machines.
What pressure range does it cover?
HydraMaster does not state the valve's adjustment range in the documentation we hold, and we are not going to publish a figure we cannot verify. Ask us if you need the specification.
My pressure collapses under trigger. Is it this valve?
That is the classic by-pass symptom, yes — but check the Y strainer screen and the orifice first, because a restriction reads similarly and costs nothing to rule out.
Chasing a pressure fault? Tell us the machine and exactly what the gauge does at rest, at trigger and on by-pass, and we will help you narrow it down before you order anything.
