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Issue with Hill Mk4 Hand Pump

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Gear_Junkie

Gear_Junkie

Member
Jan 10, 2018
818
232
CA, United States
I'm having an issue with a Hill Mk4 Hand Pump. I disassembled the pump and lubed all of the O-rings for maintenance purposes after about 4 months of light use. I just did it again after another 4 months of light use. The pump worked great for a few days and was very smooth to pump. I am now having an issue where the pump wants to spring back down as I am pulling the handle up. Also, it seems like a small amount of air is pumped on one down stroke, and then a much larger amount of air is pumped on the next stroke, and this cycle repeats. I typically only pump up to about 180 bar. Does anyone have any ideas on how to resolve this issue?



Thanks!
 
Nice! I’m glad to hear you got it working. Knowing where to look in these pumps can be daunting sometimes because there are so many seals. Fortunately the final stage O-ring is usually easy to diagnose.

I’ll go ahead and mention the second most common symptom I’ve run into (across multiple brands) is a failure to draw in air on the upstroke. That’s usually either the inlet’s check valve (typ. a rubber ball) or a fat O-ring which sits up top that’s exposed when you remove the outer tube.

For the former, note both the ball and the pocket in which it rests should be clean and dry. No silicone oil or any other lubricant because lube interferes with its ability to move freely. Mold flashing on the rubber ball or debris on the seat or a poorly machined seat will also cause this symptom. 

For the latter, the O-ring sits in a wide groove so it can move up and down, and to function correctly it needs to be sized for a snug fit on the OD and loose on the ID.
 
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Nice! I’m glad to hear you got it working. Knowing where to look in these pumps can be daunting sometimes because there are so many seals. Fortunately the final stage O-ring is usually easy to diagnose.

I’ll go ahead and mention the second most common symptom I’ve run into (across multiple brands) is a failure to draw in air on the upstroke. That’s usually either the inlet’s check valve (typ. a rubber ball) or a fat O-ring which sits up top that’s exposed when you remove the outer tube.

For the former, note both the ball and the pocket in which it rests should be clean and dry. No silicone oil or any other lubricant because lube interferes with its ability to move freely. Mold flashing on the rubber ball or debris on the seat or a poorly machined seat will also cause this symptom. 

For the latter, the O-ring sits in a wide groove so it can move up and down, and to function correctly it needs to be sized for a snug fit on the OD and loose on the ID.
Click to expand...

Good info there - thank you!
 
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hi nervoustrig question if you don't mind. i am trying to understand the second most common symptom. i have the hill mk4 hand pump and my pump seems to not suck air into the pump but it bounces right back up. it doesn't seem to want to stay down. where is that flat o-ring located that you are talking about. i have already cleaned the 2 balls that are located on top of pump. seems to be working a little better but not like i remember when it was new. can you please help me out.

hill pump.jpg
 
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Green_Yamo said:
I'm having an issue with a Hill Mk4 Hand Pump. I disassembled the pump and lubed all of the O-rings for maintenance purposes after about 4 months of light use. I just did it again after another 4 months of light use. The pump worked great for a few days and was very smooth to pump. I am now having an issue where the pump wants to spring back down as I am pulling the handle up. Also, it seems like a small amount of air is pumped on one down stroke, and then a much larger amount of air is pumped on the next stroke, and this cycle repeats. I typically only pump up to about 180 bar. Does anyone have any ideas on how to resolve this issue?



Thanks!
Click to expand...
Exact same symptoms for my Mk4 pump. Will try cleaning/lubing the small green seal/o-ring to see if it resolves my pump's issue.
 
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If it pushes back up on the bottom of the stroke, then the little check valve at the bottom of the pump is not sealing. Undo the whole pump handle from the base by loosening the bottom most nut. Unscrew the whole handle and there will be a flathead screw at the bottom. Take it out and clean off the oring and inside part where it seals. Alot of gunk builds up down there. Only has to be flush when screwed back in. Reassemble the pump handle and good to go.
 
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pumpmonster said:
hi joe tried what you told me to do and still doesn't work. now i have a bigger problem. i lost one of those little black buna balls that set in the holes on the top part of the pump. i have been looking for it now for 2 hours. no exaggeration! maybe longer
Click to expand...
I did the EXACT same thing back when I had a Mark 3. I couldn't find the bugger. I contacted Hill and they send me a couple spares. Good Luck!

Did you try vacuuming the area and searching through the bag/cannister?
 
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Green_Yamo said:
I did the EXACT same thing back when I had a Mark 3. I couldn't find the bugger. I contacted Hill and they send me a couple spares. Good Luck!

Did you try vacuuming the area and searching through the bag/cannister?
Click to expand...
hi joe; found it plus i ordered some from a company. just in case it happens again. if you need some or if you know someone who might need a couple please let me know. also after i found it i took it all apart again. took my sweet old time like i was making the pump from scratch put it all back together and nah da. i bet i must of took it apart 16 times. anyhow i'm lost for words. called Shane at AOA told me what to do and still nah da. i have a electric pump but i wanted and extra in case something would happen. Anymore idea's i'm all ears thanks joe
 
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