The distribution of valves in the veins can vary greatly.
Relationship of Common Vascular Anatomy to Cannulated Catheters (Hindawi, 2017):
Veins of the antecubital fossa [anterior side of the elbow] were much less
likely to have valves, whereas veins of the hand and forearm were
nearly equal in the frequency of valves identified. In those vein
segments of the hand with valves, there were often multiple valves
identified within the 10 cm segment studied.
The Table 2 says that in adults the average distance between the vein valves in the hand is 6 cm, in the forearm 7 cm and at the front of the elbow 17 cm.
The great saphenous vein in the inner thigh is commonly used as a graft to replace atherosclerotic coronary arteries.
The Relative Position of Paired Valves at Venous Junctions Suggests Their Role in Modulating Three-dimensional Flow Pattern in Veins (European Journal of Vascular and Endovascular Surgery, 2012)
All studied valves were located between 3 and 5 cm apart. The mean
distance between the two valves in the GSV [great saphenous vein] was
3.8 ± 0.4 cm...
Lower Extremity Venous Anatomy (Seminars in Interventional Radiology, 2005):
The number of deep venous valves increases from cranial to caudal.
Unlike the infrainguinal veins, the iliac veins rarely contain valves.
Detailed anatomic dissections have shown valves to be present in only
1.2% of common iliac veins, 27% of external iliac veins (39.6% on the right versus 14.6% on the left), and 10.1% of internal iliac veins.
There are on average five deep venous valves between the inguinal
ligament and popliteal fossa, although the number varies from two to
nine. Their arrangement is variable, but the external iliac and common
femoral vein above the saphenofemoral junction usually have one valve
at most; the femoral vein above the adductor canal has three or more
valves; the distal superficial femoral and popliteal veins have one or
two valves; and the tibial/peroneal veins have numerous valves
spaced at ∼2-cm intervals.
The small saphenous vein at the back of the lower leg:
The anatomy of the small saphenous vein: Fascial and neural relations, saphenofemoral junction, and valves (Journal of Vascular Surgery, 2010)
A most proximal valve was present in only 94% at a mean distance of
1.2 cm to the small saphenous vein orifice [popliteal vein behind the knee]. A consecutive distal valve was only present in 65% with a
mean distance of 5.1 cm.